Short answers, pulled from the story.
The Star Wars Expanded Universe is the collective name for non-film Star Wars material produced before 2014, including novels, comics, and video games. On the 25th of April 2014, Lucasfilm rebranded it as Star Wars Legends and declared it non-canonical, with the exception of The Clone Wars television series.
The first Star Wars spin-off was a novelization of the 1977 film, published in 1976 under the title Star Wars: From the Adventures of Luke Skywalker. It was ghostwritten by Alan Dean Foster.
The Holocron is a continuity database developed by Leland Chee at Lucas Licensing beginning in 2000. It tracks over 55,000 entries for franchise characters, locations, species, and vehicles, and was named after ancient repositories of knowledge within the Star Wars universe itself.
Timothy Zahn's 1991 novel Heir to the Empire reached number one on The New York Times Best Seller list and ended the franchise's output drought that had lasted since 1987. It introduced Grand Admiral Thrawn and Mara Jade, and its commercial success is credited with revitalizing the Star Wars franchise and is considered a factor in George Lucas's decision to develop the prequel trilogy.
Disney acquired Lucasfilm on the 30th of October 2012. The acquisition led to the formation of the Lucasfilm Story Group, which restructured the franchise canon, declared most prior Expanded Universe works non-canonical as Star Wars Legends in 2014, and commissioned new canonical novels, comics, and series aligned with the planned sequel trilogy.
By 2004, more than 1,100 Star Wars titles had been published across novels, comics, non-fiction, and magazines. Howard Roffman, then president of Lucas Licensing, estimated that more than 65 million Star Wars books were in print at that time.