# Coherence

Coherence is, in general, a state or situation in which all the parts or ideas fit together well so that they form a united whole.
More specifically, coherence, coherency, or coherent may refer to the following:

## Physics

* Coherence (physics), an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference
* Coherence (units of measurement), a derived unit that, for a given system of quantities and for a chosen set of base units, is a product of powers of base units with no other proportionality factor than one
* Coherence time, the time over which a propagating wave (especially a laser or maser beam) may be considered coherent; the time interval within which its phase is, on average, predictable

## Mathematics

* Coherence (philosophical gambling strategy), a concept in Bayesian statistics
* Coherence (signal processing), a statistic that can be used to examine the relation between two signals or data sets
* Coherence (statistics), a property of self-consistency across a set of assessments, or the strength of association between two series
* Coherence condition in category theory, a collection of conditions requiring that various compositions of elementary morphisms are equal
* Coherency (homotopy theory) in homotopy theory and (higher) category theory
* Coherent sampling, a relationship used in Fast Fourier transforms
* Coherent set of characters in representation theory, a property of sets of characters that allows one to extend an isometry from the degree-zero subspace of a space of characters to the whole space
* Coherent sheaf, a specific class of sheaves having particularly manageable properties closely linked to the geometrical properties of the underlying space
* Mutual coherence (linear algebra), sometimes referred to as coherence, the maximum absolute value of the cross-correlations between the columns of a matrix
* Multi-spectral phase coherence, a generalized nonlinear cross-frequency phase coupling metric introduced by Yang et al., 2016
* Coherence (fairness), a consistency requirement of fair division rules.

## Philosophy

* Coherentism, philosophical theories in modern epistemology, the study of knowledge
* Coherence theory of truth, a theory which regards truth as coherence within some specified set of sentences, propositions or beliefs

## Computer science

* Coherence (programming language), an experimental programming language based upon Subtext
* Cache coherence, a special case of memory coherence
* Memory coherence, a concept in computer architecture
* In scrum and agile methodologies, coherence is defined as a measure of the relationships between backlog items which make them worthy of consideration as a whole.

### IT products

* Coherence (software), a component of Parallels Desktop for Mac, the Windows virtualization software
* Coherent (operating system), a UNIX-clone operating system
* Oracle Coherence, an in-memory data grid product from Oracle

## Other uses

* Coherence (cognitive science), a property of mental/cognitive states
* Coherence (linguistics), what makes a text semantically meaningful
* Coherence (music theory), a synonym for strict Rothenberg propriety in diatonic set theory
* Coherent optical module, a hot-pluggable optical transceiver implementing a coherent modulation algorithm
* Coherence time (communications systems), duration when a communication channel can be assumed to be constant
* Coherent, Inc., a company specializing in equipment to make and measure coherent light (lasers)
* Coherent risk measure in financial economics, a function that satisfies properties of monotonicity, sub-additivity, homogeneity, and translational invariance
* Coherence (film), a 2013 science fiction film by James Ward Byrkit
* Sense of coherence, a construct in the health theory salutogenesis
* Policy coherence for development, a concept in development cooperation