Describes the behavior of a program that malfunctions and goes catatonic, but doesn't actually crash or abort. See glitch, bug, deep space, wedged.
This term is much older than computing, and is (uncommon) slang elsewhere. A trolley is the small wheel that trolls, or runs against, the heavy wire that carries the current to run a streetcar. It's at the end of the long pole (the trolley pole) that reaches from the roof of the streetcar to the overhead line. When the trolley stops making contact with the wire (from passing through a switch, going over bumpy track, or whatever), the streetcar comes to a halt, (usually) without crashing. The streetcar is then said to be off the trolley, or off the wire. Later on, trolley came to mean the streetcar itself. Since streetcars became common in the 1890s, the term is more than 100 years old. Nowadays, trolleys are only seen on historic streetcars, since modern streetcars use pantographs to contact the wire.