Star Trek and Star Wars have more in common than just sweaty nerds in costumes. They have sweaty nerds in costumes arguing over tiny nuances in their series' details. The term canon comes to us from religion, and like religion, it causes people to go to war over seemingly tiny details in their faith. Canon originally referred to the scriptures that were included in the various religious texts. Much like Star Wars, the core writings were handed down from an all knowing, infallable creator, but people kept adding to them. Canon is created by the church, or in this case LucasArts, to define which of these stories are in line with the faith and should be included. George Lucas does not regularly intervene in the lives of us mortals anymore, and therefore we must use the rules set up to determine what is canon and what is not.