The Star Wars Expanded Universe, called the EU for short, is the name used to denote the Star Wars books, comics, video games, and more that were part of the Star Wars canon prior to April 25, 2014. The EU began in 1978 with the release of Splinter of the Mind's Eye, and has spanned thousands of in-universe years since then. Notable EU works include the Thrawn Trilogy by Timothy Zahn, The New Jedi Order series, the video games Knights of the Old Republic and Star Wars: The Old Republic, the comic series Star Wars: Legacy, and more.
With the advent of the sequel trilogy and other new Star Wars films, it was announced that the new films will not follow the EU continuity, and that the EU would no longer be considered official canon. Moving forward, official canon will include the Star Wars films, television shows, books (beginning with A New Dawn), and more that are released as part of one unified continuity. Stories from the Expanded Universe, although not official canon, will continue to be printed and sold under the Legends banner their denote its canonical status.