# Domain

### From Conservapedia

A **domain** is the set of points where a mathematical function is defined. When the function is a function of a complex variable, a domain is usually an open connected set.

Domains are useful in many fields of mathematics, including the study of analytic and harmonic functions.

In algebra, a domain is a commutative ring *R* with identity without zero divisors: that is, for every , if *a**b* = 0, then *a* = 0 or *b* = 0.