Modular System

A set $M$ of all Polynomials in $s$ variables, $x_1$, ..., $x_s$ such that if $P$, $P_1$, and $P_2$ are members, then so are $P_1+P_2$ and $QP$, where $Q$ is any Polynomial in $x_1$, ..., $x_s$.

See also Hilbert's Theorem, Modular System Basis