Closed Interval

An Interval which includes its Limit Points. If the endpoints of the interval are Finite numbers $a$ and $b$, then the Interval is denoted $[a,b]$. If one of the endpoints is $\pm\infty$, then the interval still contains all of its Limit Points, so $[a,\infty)$ and $(-\infty, b]$ are also closed intervals.

See also Half-Closed Interval, Open Interval