Canon is a term used to designate what is considered "official" in a certain fictional universe. Unless OP allowes to use Non-canon material, only canon material can be used in a debate thread. Non-canon material doesn't count.
It's generally agreed that the work by the original author and creator of the fictional setting is canon, unless the author or the copyright holder declares otherwise.
For most manga series, the original manga is canon, while the anime is not. Databooks are considered secondary canon since scans tend to contradict them or author just doesn't understand what he's talking about (I'm looking at you Kishi)
An exception is Tenchi Muyo! Ryo Ohki/GXP/Dual! Parallel Trouble Adventure series, where the OVAs are canon since they are the original work of the author, and the manga is written by a completely different person and is not canon. Also Tengen Toppa Gurren Lagann anime is canon while movies and manga aren't.
It should also be noted that:
- In Dragon Ball only the manga, TV special "Yo! Son Goku and his Friends Return!" (because it was written by Toriyama) and MMORPG Dragon Ball Online (only partially due to Toriyama's involvement) are canon, meaning that anime (DBZ), movies and GT aren't canon.
- In Star Wars, both movies and Star Wars Expanded Universe (EU) are canon.