From The TV IV

A webisode is a short episode of a television series available online to watch either through streaming video or download. Due to increased amount of households with broadband connections, internet-based television has become a more prevalent marketing strategy for popular television series. However, this trend dates back into the late 1990s with WB Animation spin-off series like Gotham Girls and Lobo, as well as a follow-up "season" of The Critic which all took advantage of Flash and other animation technology.

Webisodes are typically far shorter than an average episode; between 2 or 5 minutes. Because of their length, the episodes are typically serialized in order to make up one or more larger episodes. In the 2000s, due in part to the surge of popularity in video iPods and other digital media devices, mainstream networks have found valid use in web content, moving prominent live-action series into the forum of internet-only episodes. Live-action series that have made use of webisodes include The Office and Eureka.