Quasi-identity

In universal algebra, a quasi-identity is an implication of the form
where "s"1, ..., "s""n", "t"1, ..., "t""n", "s", and "t" are terms built up from variables using the operation symbols of the specified signature.
A quasi-identity amount to a conditional equation for which the conditions themselves are equations. Alternatively, it can be seen as a disjunction of equations "s"1 = "t"1 ∨ ... ∨ "s""n" = "t""n" ∨ "s" = "t". A quasi-identity for which "n" = 0 is an ordinary identity or equation, whence quasi-identities are a generalization of identities. Quasi-identities are special type of Horn clauses.
See also.
Quasivariety