## ring- (MATH) Another name for an annulus.
- (MATH) A set
(see set theory) with the following
properties: it has two binary operations, addition
and multiplication (+ and ×);
it is an Abelian group under addition;
multiplication is associative, and
distributive over addition; and
*a*and*b*are members of the set,*a*×*b*has a unique value*c*, also a member of the set. If there is a member*n*of the set such that*a*×*n*=*a*for every member*a*of the set, the ring is a**ring with unity**. A ring in which multiplication is commutative is a**commutative ring**.
Compare with field.
• ALGEBRA - (ASTRON) See planetary ring.
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