As an abstract term, congruence means similarity between objects.

• In arithmetic and algebra, congruence refers to a congruence relation.
• In geometry, congruence refers to the equivalence of shapes. See congruence (geometry).
• In psychology and NLP, congruence could be defined as rapport within oneself, or internal and external consistency, perceived as sincerity.
• In cladistics, congruence is a test of homology, or shared, derived character states, in which the distributions of supposed homologies among taxa are compared for consistency.