Canon

Disclaimer
'''This is taken directly from Dragon Universe Wikia. Credit goes to them for this page'''

Summary
Dragon Ball canon (正史, seishi; Literally meaning "official history") was first officially defined during the Tokyo Skytree + Viz North America Tour in an exhibit called the History of Dragon Ball. It was later reaffirmed in December 2018 in Weekly Shōnen Jump.

As of the start of this tour on November 1, 2018, the official canon of Dragon Ball includes Akira Toriyama's original Dragon Ball manga (which composes both Dragon Ball and Dragon Ball Z manga in the West) and the Dragon Ball Super manga, which has its story written by Toriyama and artwork drawn by Toyotarō.

Additionally, despite not being adapted by the Dragon Ball Super manga as Dragon Ball Z: Battle of Gods was, Toriyama has confirmed that the events of Dragon Ball Z: Revival of "F" are a canonical continuation of his manga, as well. He also considers the Jaco the Galactic Patrolman manga and its extra chapter, Dragon Ball Minus, to be connected to his series. Most recently, Toriyama added Broly and Gogeta into the Dragon Ball canon with Dragon Ball Super: Broly.

Canon Story Arcs
During the History of Dragon Ball exhibit at the Tokyo Skytree + Viz North America Tour, official names were given for each of the canon story arcs in both the Dragon Ball and Dragon Ball Super manga.

Akira Toriyama and Dragon Ball Canon
Akira Toriyama is the original creator and author of the Dragon Ball manga. Over the years, Toriyama has made numerous claims about the canon status of various medias set within his franchise. It is clear from these comments—and from others, in which he derides both the Japanese and English anime adaptations for their portrayal of Son Goku—that he defines the canon of Dragon Ball as being in relation to his original manga.

On the Dragon Ball and Dragon Ball Z movies, Toriyama stated:

"I take the movies as “stories in a different dimension from the main story of the comic”. I’m entirely just an audience member for them."

On Dragon Ball Z: Battle of Gods and Dragon Ball Z: Revival of "F", Toriyama stated that:

"[As with the last movie], I thought up the new story for the next Dragon Ball theatrical film as though it were a continuation of the manga when it was in serialization."

However, in November 2018, Toei Animation and Shueisha Publishing Co., Ltd. confirmed during the Tokyo Skytree + Viz North America Tour that the Dragon Ball Super manga, for which Toriyama was responsible for only the story and character designs, was canon to Toriyama's manga.

Canon and the Extended Universe
The Dragon Ball franchise consists of a vast variety of media including various anime, films, video games, and even other manga series. This can make it difficult to discern the canonicity of certain content. However, as of the Tokyo Skytree + Viz North America Tour's History of Dragon Ball exhibit, it is confirmed that only the Dragon Ball and Dragon Ball Super manga, with the addition of Revival of "F", Jaco the Galactic Patrolman, and Dragon Ball Minus, are considered canon to Toriyama's franchise.

Anime and Canon
The Dragon Ball anime, Dragon Ball Z, Dragon Ball Z Kai, and Dragon Ball Super anime all adapt content from their respective manga series. As a result, the adapt and depict canon content. However, they also depict original content that falls outside the preview of canon (i.e., the Garlic Junior Arc).

Anime series like Dragon Ball GT have been treated as sequels to the Dragon Ball franchise, but are not, in fact, official sequels to Akira Toriyama's manga. Other anime series, like the Dragon Ball Heroes anime are purely promotional material for its corresponding video game franchise and are not meant to be interpreted as official continuations of Toriyama's manga.

Films and Canon
With the exceptions of God and God and Revival of "F," which Akira Toriyama declared to be official continuations of his manga, movies are considered to be different stories set in other dimensions. As a result, Dragon Ball and Dragon Ball Z animated films are not considered canonical.

Games and Canon
While games frequently adapt canon content, they are not in anyway meant to be considered canonical. This includes Dragon Ball Online, which, unlike most video games, was heavily worked upon by Akira Toriyama, but was never officially released outside of Korea.

Canon and Dragon Ball GT
The canon status of Dragon Ball GT has been an issue of contentious debate among the Dragon Ball fan community. As both Dragon Ball and Dragon Ball Super proceed the story of Dragon Ball GT by many years, there are no direct contradictions with the story of GT.

Akira Toriyama had the following to say about the anime-only adaptation:

"Being a lazy bum by nature, I was absurdly happy when I managed to safely finish up Dragon Ball’s serialization, and finally be released from Deadline Hell. The TV anime people wanted to continue for just a little bit more, but I [just couldn’t do] any more than that… And so, I left the Dragon Ball anime completely up to the anime staff, story and all. That was Dragon Ball GT.... Dragon Ball GT is a grand side-story of the original Dragon Ball, and it’ll make me happy for us to watch and enjoy it together."

[https://www.kanzenshuu.com/translations/dragon-book-gt-toriyama-intro/ Furthermore, GT is the Dragon Ball media with the least amount of involvement from Toriyama. Toriyama himself only came up with the title for the series, designed the main cast and their vehicles, and he drew a few pictures for the series.]

As a result of these facts in conjunction with its exclusion from the Tokyo Skytree + Viz North America Tour's History of Dragon Ball exhibit, Dragon Ball GT is not considered canon to the Dragon Ball manga.

Reference Books and Canon
[http://www.kanzenshuu.com/production/toriyama/ Reference books, like the Daizenshū series, often expand upon content that is not touched upon or fully explained in the anime, films, or the manga. However, like the aforementioned Daizenshū series of databooks, most Dragon Ball reference books are anime reference books and have little to no involvement from Akira Toriyama himself. Therefore, they are supplemental to the anime, but are not considered to be canonical.]

However, there are exceptions. Toriyama condones its use and says the Daizenshuu is more credible on the series than himself. Source for this picture and the below translation, as well as a source that Toriyama is an author of the Daizenshuu 7.