a cat burglar generally refers to a thief who breaks into homes to steal personal property. Cats are stealthy and quiet, approaching prey without causing alarm, pouncing without warning. A cat burglar is a thief who slips in unnoticed, taking what he wants before the victim knows whats happened. A cat burglar might also be associated with theft from outbuildings such as sheds, barns or garages, automobiles, boats, planes, trains, churches or schools.
In a wider sense, a cat burglar is simply a thief, foremostly associated with breaking and entering a legal term.