Equivalence Relation

A Dictionary of Philosophy, Third Edition

. Any SYMMETRIC AND TRANSITIVE relation, e.g. equal in size to.

Its terms are equivalent in the sense that there is some determinable property, like size, which they all have to the same degree or in the same determinate form, and whatever any of them has the relation to, so do the others. If a is equal in size to b, then if a is equal to c, b also is equal to c.