Page "Commutative ring" Paragraph 15

In contrast to fields, where every nonzero element is multiplicatively invertible, the theory of rings is more complicated.

There are several notions to cope with that situation.

First, an element a of ring R is called a unit if it possesses a multiplicative inverse.

Another particular type of element is the zero divisors, i. e. a non-zero element a such that there exists a non-zero element b of the ring such that ab = 0.

If R possesses no zero divisors, it is called an integral domain since it closely resembles the integers in some ways.