user: What is Glossary and how is it used in Blender Python scripting?

assistant: # Glossary

This page lists definitions for terms used in Blender and this manual.

[Action](../animation/actions.xhtml)
:   Blender’s container for animation data. In Blender, animatable [data-blocks](#term-Data-Block) do not store
    their own animation data, but instead store their animation data an actions.

Action Safe
:   Area of the screen visible on most devices. Place content inside it to ensure it does not get cut off.

Active
:   When many items are selected, the last selected item will be the active one.
    Used in situations where the interface only shows options for one item at a time.

    See also [selection states](../scene_layout/object/selecting.xhtml#object-active).

Aliasing
:   Rendering artifacts in the form of jagged lines.

Alpha Channel
:   Additional channel in an image for transparency.

    Straight Alpha
    :   Method where RGBA channels are stored as (R, G, B, A)
        channels, with the RGB channels unaffected by the alpha channel.
        This is the alpha type used by paint programs such as Photoshop or Gimp,
        and used in common file formats like PNG, BMP or TARGA.
        So, image textures or output for the web are usually straight alpha.

    Premultiplied Alpha
    :   Method where RGBA channels are stored as (R × A, G × A, B × A, A),
        with the alpha multiplied into the RGB channel.

        This is the natural output of render engines, with the RGB channels representing the amount
        of light that comes toward the viewer, and alpha representing how much of the light from
        the background is blocked. The OpenEXR file format uses this alpha type. So, intermediate files
        for rendering and compositing are often stored as premultiplied alpha.

    Conversion (Straight/Premultiplied) Alpha
    :   Conversion between the two alpha types is not a simple operation and can involve data loss,
        as both alpha types can represent data that the other cannot, though it is often subtle.

        Straight alpha can be considered to be an RGB color image with a separate alpha mask.
        In areas where this mask is fully transparent, there can still be colors in the RGB channels.
        On conversion to premultiplied alpha, this mask is *applied* and the colors in such areas
        become black and are lost.

        Premultiplied alpha, on the other hand, can represent renders that are both emitting light
        and letting through light from the background. For example, a transparent fire render might
        be emitting light, but also letting through all light from objects behind it.
        On converting to straight alpha, this effect is lost.

    Channel Packed
    :   A separate image map is stored for each color and alpha channel.
        Channel packing is commonly used by game engines to save memory and to optimize memory access.

Ambient Light
:   The light that comes from the surrounding environment as a whole.

Ambient Occlusion
:   A ratio of how much [Ambient Light](#term-Ambient-Light) a surface point would be likely to receive.
    If a surface point is under a foot or table,
    it will end up much darker than the top of someone’s head or the tabletop.

Animation
:   Simulation of motion.

Anti-Aliasing
:   Is the technique of minimizing [Aliasing](#term-Aliasing), by e.g. rendering multiple samples per pixel.

Armature
:   An [Object](#term-Object) consisting of [Bones](#term-Bone). Used to [Rig](#term-Rig) characters, props, etc.

Asset
:   Curated data-blocks that are meant for reuse, usually contained in an [Asset Library](#term-Asset-Library).
    See also [Asset Libraries](../files/asset_libraries/introduction.xhtml).

    Note that there are other meanings of the word “asset” – sometimes this
    is used more generically, and refers to any “useful thing”, like images,
    models, materials, and more.

Asset Catalog
:   Container for assets, similar to what a directory is for files.
    See also [Asset Catalogs](../files/asset_libraries/catalogs.xhtml).

Asset Library
:   Directory on drive, registered in the list of asset libraries in the preferences.
    See also [Asset Libraries](../files/asset_libraries/introduction.xhtml) and [Current File Asset Library](#term-Current-File-Asset-Library).

Asset Metadata
:   Asset-related information, such as its [catalog](#term-Asset-Catalog),
    description, author, preview, and tags. See [Asset Details Region](../editors/asset_browser.xhtml#editing-asset-metadata).

Attribute
:   A generic term to describe data stored per-element in a geometry data-block.

Axis
:   A reference line which defines coordinates along one cardinal direction in n-dimensional space.

Axis Angle
:   Rotation method where X, Y, and Z correspond to the axis definition,
    while W corresponds to the angle around that axis, in radians.

Baking
:   The process of computing and storing the result of a potentially
    time-consuming calculation so as to avoid needing to calculate it again.

Bevel
:   The operation to chamfer or bevel edges of an object.

Bézier
:   A computer graphics technique for generating and representing curves.

Bit Depth
:   The exponent value (with base two) for how many colors can be represented within a single color channel.
    A higher bit depth will allow more possible colors, reducing banding, and increasing precision.
    Yet a higher bit depth will increase memory usage exponentially.

Blend Modes

Color Blend Modes
:   Methods for blending two colors together.

    See also [Blend Modes](https://docs.krita.org/en/reference_manual/blending_modes.html) on Krita docs.

Blender Session

Session
:   The timespan of a Blender instance. The session begins with starting an instance of Blender
    and ends with closing it.

    In some cases, loading a new file may be considered beginning a new
    session. If so, the documentation should mention that.

Bone
:   The building block of an [Armature](#term-Armature). Made up of a [Head](#term-Head),
    [Tail](#term-Tail) and [Roll Angle](#term-Roll-Angle) which define a set of local axes and a
    point of rotation at the Head. Also see [Pose Bone](#term-Pose-Bone).

Bone Collection
:   Collection of [bones](#term-Bone) of an [Armature](#term-Armature), identified by
    its name. Bone collections can be used to organize bones and toggle their
    visibility. See [Bone Collections](../animation/armatures/bones/bone_collections.xhtml#bone-collections).

Boolean
:   A type of logic dealing with binary true/false states.

    See also [Boolean Modifier](../modeling/modifiers/generate/booleans.xhtml).

Bounding Box
:   The box that encloses the shape of an object. The box is aligned with the local space of the object.

Bump Mapping
:   Technique for simulating slight variations in surface height using a grayscale “heightmap” texture.

BVH

Bounding Volume Hierarchy
:   A hierarchical structure of geometric objects.

    See also [Bounding Volume Hierarchy](https://en.wikipedia.org/wiki/Bounding_volume_hierarchy) on Wikipedia.

Caustics
:   The optical phenomenon of light concentration focused by specular reflections or refracting objects.
    In example observable on light passing through a glass of water onto a table or
    the pattern at the bottom of a swimming pool.

    In rendering this refers to diffuse reflected light paths after a glossy or refraction bounce.

    See also [Caustics](https://en.wikipedia.org/wiki/Caustic_(optics)) on Wikipedia.

Child
:   An [Object](#term-Object) that is affected by its [Parent](#term-Parent).

Chroma

Chrominance
:   In general, a resulting image color decomposition, where its (*L* or *Y*) luminance channel is separated.
    There are two different contexts whereas this term is used:

    Video Systems
    :   Refers to the general color decomposition resulting in *Y* (Luminance) and *C* (Chrominance) channels,
        whereas the chrominance is represented by: U = ( Blue minus Luminance ) and V = ( Red minus Luminance ).

    Matte Compositing
    :   Refers to a point in the color gamut surrounded by a mixture of a determined spectrum of its RGB
        neighboring colors. This point is called *Chroma key* and this key (a chosen color) is used to create
        an *Alpha Mask*. The total amount of gamut space for this chrominance point is defined by users
        in a circular or square-shaped format.

Chromaticities
:   The coordinates of the [Primaries](#term-Primaries) on the CIE 1931 xy chromaticity diagram.

Clamp

Clamping
:   Limits a variable to a range. The values over or under the range are set
    to the constant values of the range’s minimum or maximum.

Collection
:   A device for organizing objects. See also [Collections](../scene_layout/collections/collections.xhtml).

Color Gamut
:   A gamut traditionally refers to the volume of color a particular color model/space can cover.
    In many instances, it is illustrated via a 2D model using CIE Yxy coordinates.

Color Model
:   A mechanism for representing colors as numbers.

    RGB
    :   An additive system where three primaries; red, green, and blue are combined to make other colors.

    HSV
    :   Three values often considered as more intuitive (human perception) than the RGB system.
        In this model, colors are represented as [Hue](#term-Hue), [Saturation](#term-Saturation), and [Value](#term-Value).

    HSL
    :   Similar to *HSV* except the colors are represented as
        [Hue](#term-Hue), [Saturation](#term-Saturation), and [Luminance](#term-Luminance).

    YUV
    :   Luminance-Chrominance standard used in broadcasting analog PAL (European) video.

    YCbCr
    :   Luminance-ChannelBlue-ChannelRed component video for digital broadcast use,
        whose standards have been updated for HDTV and commonly referred to as the HDMI format for component video.

Color Space
:   A color space is a coordinate system in which a vector represents a color value.
    The definition of a color space specifies three things:

    - The exact color of each of the [Primaries](#term-Primaries).
    - The [White Point](#term-White-Point).
    - A transfer function (also called a tone response curve).

    The color spaces available in Blender depend on the active [OCIO config](../render/color_management/opencolorio.xhtml#ocio-config).
    The default supported color spaces are described in detail at
    [Default OpenColorIO Configuration](../render/color_management/color_spaces.xhtml#ocio-config-default-color-spaces).

    Linear
    :   A linear color space means that the numerical values of the color channels are directly proportional
        to light intensity. This is the most physically accurate representation of color and is used internally
        for rendering, shading, and compositing to ensure correct blending and lighting calculations.

    sRGB
    :   A widely used display-referred color space that uses the Rec.709 [Primaries](#term-Primaries) and a D65 white point.
        It applies an approximate 2.2 gamma transfer function to better match human perception of brightness.
        sRGB is the standard for monitors, images, and the web, making it the most common format for saving
        or displaying images outside of Blender.

    - Linear color space is recommended for internal work, such as rendering and compositing.
    - sRGB is typically used for output images intended for screens and general distribution.
    - Wide gamut and high dynamic range workflows may use other color spaces, such as ACES, depending on
      the active OCIO configuration.

Concave Face
:   Face in which one vertex is inside a triangle formed by other vertices of the face.

    See also [Convex and concave polygons](https://en.wikipedia.org/wiki/Convex_and_concave_polygons)
    on Wikipedia.

Constraint
:   A way of controlling one [Object](#term-Object) with data from another.

Convex Face
:   Face where, if lines were drawn from each vertex to every other vertex,
    all lines would remain in the face. Opposite of a [Concave Face](#term-Concave-Face).

Coplanar
:   Refers to any set of elements that are all aligned to the same 2D plane in 3D space.

Crease
:   Property of an [Edge](#term-Edge). Used to define the sharpness of edges in [Subdivision Surface](#term-Subdivision-Surface) meshes.

Current File Asset Library
:   Asset library that is not a directory on drive, but only reflects the assets in
    the current blend-file. This library is available regardless of the location of
    the blend-file. See [The Current File Asset Library](../files/asset_libraries/introduction.xhtml#asset-library-current-file).

Curve
:   A type of object defined in terms of a line interpolated between Control Vertices.
    Available types of curves include [Bézier](#term-Bezier), [NURBS](#term-NURBS) and Poly.

Curve Segment
:   The part of a curve connecting two adjacent control points.

Cyclic
:   Often referring to an object being circular. This term is often associated with [Curve](#term-Curve).

Data User
:   An existing Blender object, which is using its own data, or
    linked data (data owned and controlled by another Blender object).

Data-Block
:   Data-blocks are the named items in Blender that serve as the base unit of
    data in a blend file, and which can be linked into other blend files. Some
    examples of data-blocks are objects, materials, armatures, meshes,
    node-trees, and actions.

Dielectric Material
:   A material for real world objects that are electrical insulators such as plastics, wood, glass, etc.
    Essentially this summarizes any material that is solid and non metallic.

Diffuse Light
:   Even, directed light coming off a surface.
    For most things, diffuse light is the main lighting we see.
    Diffuse light comes from a specific direction or location and creates shading.
    Surfaces facing towards the light source will be brighter,
    while surfaces facing away from the light source will be darker.

Directional Light
:   The light that has a specific direction, but no location.
    It seems to come from an infinitely far away source, like the sun.
    Surfaces facing the light are illuminated more than surfaces facing away, but their location does not matter.
    A directional light illuminates all objects in the scene, no matter where they are.

Displacement Mapping
:   A method for distorting vertices based on an image or texture.
    Similar to [Bump Mapping](#term-Bump-Mapping), but instead operates on the mesh’s actual geometry.
    This relies on the mesh having enough geometry to represent details in the image.

Display Referenced
:   Refers to an image whose [Luminance](#term-Luminance) channel is limited to a certain range of values (usually 0-1).
    The reason it is called display referenced is because a display cannot display an infinite range of values.
    So, the term [Scene Referenced](#term-Scene-Referenced) must go through a transfer function to be converted
    from one to the other.

DOF

Depth of Field
:   The distance in front of and behind the subject which appears to be in focus. For any given lens setting,
    there is only one distance at which a subject is precisely in focus, but focus falls off gradually on either
    side of that distance, so there is a region in which the blurring is tolerable. This region is greater behind
    the point of focus than it is in front, as the angle of the light rays change more rapidly;
    they approach being parallel with increasing distance.

Double Buffer
:   Technique for rendering and displaying content on the screen.
    Blender uses two buffers (images) to render the interface,
    the content of one buffer is displayed while rendering occurs on the other buffer.
    When rendering is complete, the buffers are switched.

DPI

Dots Per Inch
:   A physical measurement for the number of individual dots that can be placed in a line span of one inch.

    This term typically applies to printing however it is often used loosely to mean [PPI](#term-PPI).

    See also:

    - [Pixel Density support for image formats](../files/media/image_formats.xhtml#files-media-image-formats)
    - [Pixel Density support for render output](../render/output/properties/output.xhtml#render-output-pixel-density-panel)

Edge
:   Straight segment (line) that connects two [Vertices](#term-Vertex), and can be part of a [Face](#term-Face).

Edge Loop
:   Chain of [Edges](#term-Edge) belonging to consecutive [Quads](#term-Quad).
    An edge loop ends at a pole or a boundary. Otherwise, it is cyclic.

Edge Ring
:   Path of all [Edges](#term-Edge) along a [Face Loop](#term-Face-Loop) that share two faces belonging to that loop.

Elastic
:   Objects that are able to spontaneously return to their original shape
    after all outside forces are removed from the object.

Elasticity
:   The amount a material is elastic versus inelastic.

Empty
:   An [Object](#term-Object) without any [Vertices](#term-Vertices), [Edges](#term-Edge) or [Faces](#term-Face).

Euler

Euler Rotation
:   Rotation method where rotations are applied to each of the X, Y, Z axes in a specific order.

    Euler orders in Blender are most intuitive when read backwards: *XYZ Euler* is similar to rotating
    around *Local Z* using the *Rotate* tool in the 3D Viewport, followed by *Local Y* and then *Local X*.

F-Curve
:   A curve that holds the animation values of a specific property.

Face
:   Mesh element that defines a piece of surface. It consists of three or more [Edges](#term-Edge).

Face Loop
:   Chain of consecutive [Quads](#term-Quad). A face loop stops at a [Triangle](#term-Triangle) or [N-gon](#term-N-gon)
    (which do not belong to the loop), or at a boundary. Otherwise, it is cyclic.

Face Normal
:   The normalized vector perpendicular to the plane that a [Face](#term-Face) lies in. Each face has its own normal.

Fake User
:   A special [Data User](#term-Data-User), a program construct that is
    used to mark an object (e.g. material)