It’s very binary in the Disney era. All the theatrical movies, the 2008 Clone Wars TV show, Rebels, and all the rest of the Disney-era TV shows are canon, as are all of the novels, comics, games etc released during the Disney era. Everything else is non-canon. Lucasfilm maintains a tight grip on canon and that’s a big part of what Pablo Hidalgo’s job is all about.

Before the Disney-era, the concept of canon in the Star Wars Expanded Universe was more complicated and fluid, and relied on ‘tiers’ of canon with the movies at the top, the TV shows next, certain novels next, etc. The idea of canon back then was that anything in the one of the lower tiers could be canon as long as it wasn’t contradicted by something in a higher tier. For example, if somebody wrote an EU novel that said that Anakin loved sand, that would be non-canon because it’s directly contradicted by Attack of the Clones; but if they wrote a novel that said Padme loved sand, that might be canon if there’s nothing in the higher tiers of canon to contradict it.