Star Wars Legends, formerly known as the Expanded Universe (abbreviated EU), encompasses every one of the licensed and background stories of the Star Wars universe, outside of the original six Star Wars films produced by George Lucas and certain other material such as Star Wars: The Clone Wars, created before April 25, 2014. It is derived from and includes most official Star Wars books, comic books, video games, spin-off films, television series, toys, and other media created before that date. This material expands and continues the stories told in the films, taking place anywhere from over 36,000 years before The Phantom Menace to 136 years after Return of the Jedi.
On April 25, 2014, Lucasfilm Ltd. announced that in preparation for the upcoming sequel trilogy, the Expanded Universe would be retconned; past tales of the Expanded Universe will be printed under the Star Wars Legends banner, and a new continuity has been established that consists only of the original six films, the Star Wars: The Clone Wars television series and film, and all future material from that point onward. Though past elements of the Expanded Universe have been declared non-canon as a whole, they remain a resource for future Star Wars material to reference, thus bringing these elements into the new continuity as canon. Today, the only Legends product that is still being released is the video game Star Wars: The Old Republic, along with short stories published at the Star Wars blog.
The Expanded Universe had a continuity with a few wrinkles. The general rule was that nothing in the Expanded Universe was allowed to contradict any other part of the Expanded Universe or the films. The films, however, do slightly contradict the Expanded Universe on occasion, and retcons were created in the Expanded Universe to fix these contradictions. In the absence of such ad hoc solutions, the EU is considered incorrect only on the particular points of contradiction.
The Expanded Universe is actually older than the films themselves, as the novelization of the original film was published six months before the film was released. In in-universe chronology, the earliest works are the Dawn of the Jedi comics, which are set millennia before the films, while the latest are the Legacy comics, which are set about one hundred and thirty years after Return of the Jedi.