Kuiper Belt

The Kuiper Belt is a region just beyond the planetary system and orbit of Pluto, where numerous objects have been found in recent years, very similar in size (and probably composition) to Pluto.

Kuiper Belt objects and trans-Neptunian objects are one and the same thing. David Jewitt's site contains information on Kuiper Belt objects and current research into these elusive bodies.

Kuiper Belt / trans-Neptunian links :-
IAU Minor Planet Centre's list of trans-Neptunian objects.