correspondence

(noun) communication by the exchange of letters.

(noun) compatibility of observations. Synonyms: agreement. Examples: "There was no agreement between theory and measurement." "The results of two tests were in correspondence."

(noun) the relation of corresponding in degree or size or amount. Synonyms: commensurateness, proportionateness.

(noun) (mathematics) an attribute of a shape or relation; exact reflection of form on opposite sides of a dividing line or plane. Synonyms: symmetry, symmetricalness, balance.

(noun) similarity by virtue of corresponding. Synonyms: parallelism.