A Kuiper belt is a collection of planetoids found in the outer regions of a star system. In contrast to rocky asteroid belts, Kuiper belts tend to contain objects made of ice. Oort clouds are typically located further out from a Kuiper belt.
In 2375, Odo and the sixth clone of Weyoun attempted to evade pursuing Jem'Hadar attack ships by hiding in a Kuiper belt, taking their runabout, the USS Rio Grande, into the interior of a large chunk of ice and powering down. The Jem'Hadar forced them out of hiding by destroying every large ice chunk in range. (DS9: "Treachery, Faith and the Great River")