Chief factor ($N/M◃G/M$)

A chief factor of $G$ is a quotient $N/M$ with $M,N$ normal in $G$ and no $G$-normal subgroup strictly between them. Equivalently, $N/M$ is a minimal normal subgroup of $G/M$. Such factors are the successive factors of a chief series, and are direct products of isomorphic simple groups when $G$ is finite.