"Canon" refers to any person, term, event or so on that is regarded as an official part of the Sailor Moon universe. Or indeed universes, because there are many different versions of Sailor Moon, all bearing similarities but also showing many differences. So, which of these is regarded as "official"? Well, they all are, but it's important to keep them separate. This guide explains how to separate them appropriately.
Things That Are Canon
Some versions of Sailor Moon contain not one, but multiple continuities.
All of the anime occurs within a single continuity, and all of it is regarded as canon, including the movies and specials. The only exception is episode 89, which occurs outside normal continuity, as it involves the girls speaking directly to the viewers, acknowledging the fictitious nature of the series. Material printed in official anime guides can usually be regarded as canon too, although its use should be noted to avoid confusion.
The main story of the manga occurs within a single continuity, although there are a few micro-continuities. "Kaguya-hime no Koibito," the manga version of the Sailor Moon S movie, is one of them, and the other is "Parallel Sailor Moon." Note that Codename: Sailor V, as well as the side stories (such as the Chibiusa's Picture Diary or Exam Battle stories) are all generally regarded as occurring within the main storyline.
Each of the musicals effectively occurs within its own continuity (with the exception of the musicals of the Dracul arc, which are collectively one continuity). All of these are canon, but be sure to list them separately to avoid confusion.
The changes made to the anime in the English dub mean that it has developed a continuity of its own. Thus, all events from the dub are considered canon. However, given that these events are usually near-identical to the original, it is generally not necessary to include an "English dub" section within articles. Mentioning any differences in the notes section will usually suffice, unless there have been any particularly huge changes.
Things That Are Not Canon
There are a few sections of the Sailor Moon multiverse that, due to authorship or technical reasons, are not considered to be canon.
Video games are interactive and thus do not have a set storyline. In the case of a Sailor Moon puzzle game, for example, this wouldn't really matter as there is no plot anyway. However, games such as Sailor Moon: Another Story have original plots and characters. While these are not considered canon, we do urge contributors to include them here anyway. The only real difference, as explained below, is that they can not be spoken about from an in-universe perspective.
Specific details of individual fan works are beyond the scope of this project and thus should not be included in the wiki. Common concepts such as Otaku Senshi are mentioned, but it should be made clear that they are not part of canon.
All articles about actors, writers, and so on involved in the production of Sailor Moon are, naturally, non-canon.
What This Means
So, what does it matter whether something is canon or not? Well, firstly, it affects what perspective you have to use to talk about it. Canon events require the in-universe perspective, while non-canon events should be discussed using an out-of-universe perspective.
Understanding the different canons is also important for structuring articles. It is not a good idea to lump all continuities into the same paragraph. A good article will be divided into separate sections, each one dealing with its subject in a different continuity.
All Continuities Are Equal...
But some are more equal than others.
While we welcome articles derived from every Sailor Moon continuity, there are certain continuities that, for technical reasons, must take precedence over others. This is especially important as regards the information put within infoboxes.
Primary and Lesser Continuities
The three primary continuities here are the anime, PGSM and the main continuity of the manga (incorporating Sailor V as well as the Chibiusa's Picture Diary and Exam Battle short stories). These are the largest and most well-recognized continuities. The lesser continuities are the musicals and the manga side-continuities ("Kaguya-hime no Koibito" and "Parallel Sailor Moon"). While the musicals together account for a large proportion of series canon, they are effectively all small, unrelated sub-continuities.
When filling in an infobox, only include information from the three primary continuities. Information from other continuities is welcome, but restrict it to the main body of the article. The only case when information from lesser continuities should be included in an infobox is when the subject of the article occurs only within that continuity: for example, a musical-only character such as Loof Merrow.