Definition:Real Interval

Definition
Informally, the set of all real numbers between any two given real numbers $a$ and $b$ is called a (real) interval. There are many kinds of intervals, each more-or-less consistent with this informal definition.

Also see

 * Equivalence of Definitions of Real Interval
 * Real Number Line is Metric Space

Generalizations

 * Definition:Open Rectangle, a generalization to higher dimensional spaces
 * Definition:Half-Open Rectangle