An algebra with a constant term $e$ is \emph{congruence $e$-regular} if each congruence relation of the algebra is determined by its $e$-congruence class, i.e., for all congruences $\theta$, $\psi$ of the algebra $[e]_{\theta}=[e]_{\psi}\Longrightarrow \theta =\psi$.

A class of algebras is \emph{congruence $e$-regular} if each of its members is congruence $e$-regular for a fixed constant term $e$ in the language of the class.

Congruence $e$-regularity holds for many 'classical' varieties such as groups, rings and vector spaces.

This property can be characterized by a Mal'cev condition …