A juggler was an entertainer skilled in the manipulation of objects, usually by throwing them in the air and catching them before they hit the ground.
Lwaxana Troi's Parallax colony holoprogram included a hologram of a juggler. In 2368, she brought Alexander Rozhenko into the program to relax during her visit to the USS Enterprise-D. The juggler referred to his juggling balls as "worlds", and ended up eating them after catching one in his mouth and seeing that it tasted good. (TNG: "Cost of Living")
Ensign Pablo Baytart, a Starfleet officer aboard the Federation starship USS Voyager, was a skilled juggler and was one of the first featured guests on A Briefing with Neelix, in 2372. In his appearance he juggled a collection of PADDs, hyposprays and phasers. (VOY: "Investigations")