Canon means that something is true to the story. In Bleach this means that it happened in the Bleach universe. The main source for canon material is the manga. The anime is a secondary source, as long as something in the anime does not contradict the manga then it is canon. No movies or special are canon - with the exception of "Memories in the Rain" OVA, which is not only based on manga chapters but follows the manga chapters more closely then the same events as depicted in the anime.