interval
A set of real numbers bounded by two real numbers - the endpoints or bounds. The set may or may not include either endpoint, leading to four possibilities:
closed [a, b] a <= x <= b open (a, b) a < x < b left-open, right-closed (a, b] a < x <=b left-closed, right-open [a, b) a <= x < b
See closed interval, open interval.