IntervalUnion

IntervalUnion[interval1, interval2, ...] gives an interval containing points in any of the intervals.

Examples

Combine overlapping intervals:

IntervalUnion[Interval[{0, 5}], Interval[{3, 10}]]
(* Interval[{0, 10}] *)

Combine disjoint intervals:

IntervalUnion[Interval[{0, 2}], Interval[{5, 10}]]
(* Interval[{0, 2}, {5, 10}] *)

Please visit the official Wolfram Language Reference for more details.