Tangent space uses vectors from the mesh data to stay relative to the surface of the mesh. It can be difficult to visualise for an entire model as unlike other spaces, it can be different per-pixel. A way to visualise the tangent space for a given point (centered at the gizmo) The Normal vector you should be familiar with, points out from each vertex - It’s the Z axis of tangent space (shown in blue, since XYZ=RGB). The X and Y axis use the Tangent vector and a Bitangent vector (also called Binormal) - which is typically calculated using a Cross Product with the other two vectors. These tangent and bitangent vectors are also aligned to the direction of the UV coordinates stored in the mesh. (The tangent follows the X axis of the UV coordinates, and the bitangent follows the Y axis) The space is needed so tangent space normal maps (that use UV coordinates for sampling) can be converted back to world space to produce correct lighting/shading. The tangent space View Direction is also used to produce Parallax effects. Of note, if you are using techniques like Triplanar Mapping, then the “Tangent space” you’d need would be different than the Tangent space calculated from mesh data. This article by Ben Golus explains this in detail. In Shader Graph, the Triplanar node already takes this into account when using it’s Normal mode (I believe using the “Whiteout Blend” example)