Episode

An episode in ZDoom is technically just a way to define a starting map for a new game, through the episode selection menu.

The term episode is also commonly used to define a cluster of levels. For example, The Ultimate Doom provides four nine-level episodes which are played independently, while Doom II provides four episodes (and two secret maps) which are played in sequence, the first episode going from MAP01 to MAP06, the second from MAP07 to MAP11, the third from MAP12 to MAP20, and the last from MAP21 to MAP30. (Though the first two are often considered a single episode since they use the same sky.) When an episode is completed, the intermission screen explains how the story advanced and prepares for the next episode.