1.NounA subset of a ring which contains the ring’s unity and which is multiplicatively closed, i.e., it is closed with respect to the ring’s multiplicative operation.
"If
P
{\displaystyle P}
is a proper prime ideal of a ring and
M
{\displaystyle M}
is the set complement, w.r.t. the ring, of
P
{\displaystyle P}
, then
M
{\displaystyle M}
is a multiplicative subset."