Hulu is a Web video service from NBC Universal and Fox Entertainment Group. Designed as a deterrent for online privacy, Hulu lets users watch full-length movies and TV shows right in their browser, and with limited commercials and other on-page advertising.
Unlike sites like YouTube, everything on Hulu comes directly from the content providers, and not from users. Another thing that sets it apart from most other video sites, is that content is set to expire after a certain amount of time on the service. This is in part to encourage users to watch programming while it's on TV, as well as boost DVD sales.
Hulu is currently limited to desktop computers, however a mobile version is rumored to be on the way later this year.