A wormhole is a hypothetical tunnel through space-time which may be traversable and allow matter (such as a spaceship or person) to travel very quickly between two places in the universe that are normally very far apart. The term was introduced in 1957 by physicist John Wheeler, and derives from a "real world" example used to describe the phenomenon. Imagine a worm crawling around an apple; if it burrows straight through the apple to the other side it will get there faster. A wormhole traveller takes a similar shortcut through the universe.
Although they are still hypothetical in science, wormholes have long been staples of science fiction, allowing characters to travel quickly from one side of the Galaxy or Universe to the other, and sometimes even through time. Wormholes are an integral part of the Farscape universe.
At the beginning of Farscape, Crichton travels through a wormhole from earth, and finds himself in the middle of Moya and Pilot's escape from the Peacekeepers. It later becomes apparent that he has the knowledge of wormhole technology in his head, something that Scorpius would very much like to have for himself.