Episodic Content

Episodic content is when the publishers of a game decide to release a game in multiple parts or episodes. Episodes are usually shorter than full games and not as expensive. Usually once all the episodes are out, the publisher releases a package with all the episodes. 
Episodic content is said to have originated from a company known as Apogee (now known as 3D Realms). This game company began distributing their games in episodes, offering discounts to people who bought multiple episodes at once. It would give out the first episode for free, then make the customer pay for the rest. This was called the Apogee Model.