congruence

The quality of agreeing or corresponding; being suitable and appropriate.

(mathematics, number theory) A relation between two numbers indicating they give the same remainder when divided by some given number.

(mathematics, geometry) The quality of being isometric — roughly, the same measure and shape.

(mathematics, linear algebra) Matrix similarity by an orthogonal matrix.

(algebra) More generally: any equivalence relation defined on an algebraic structure which is preserved by operations defined by the structure.