A gadabout is someone who's constantly on the move, looking for the most fun social activity they can find. If there are four parties on Saturday night, a gadabout will make it to all of them.
Gadabouts are known for their restless tendency to wander from place to place, and for being pleasure seekers. It can be hard to take a gadabout seriously, since having fun is their highest priority. This noun first appeared in the 19th century, from an earlier phrase, gadder about, "walk around idly," and the now obsolete verb gad, "wander randomly and frivolously."