It's not a Pokemon. Well maybe it is...but we're not talking about the Pokemon right now!!
A Wikitag is a content-type used on LessWrong that combines a wiki-page and a tag into a single entity/abstraction. We think this just makes sense.
Take the concept of Functional Decision Theory. We could separately have a wiki page that explains the concept and a tag that is applied to posts about that concept, but why have them be separate? If the wiki page is also a tag, then we can conveniently list on it all the posts that are relevant.
True! And that's why wikitag pages come with a checkbox for whether or not a given wikitag should be usable as a tag.
Some reasons a wiki page shouldn't be usable as a tag:
The decision for whether a wikitag page should have the tag-component activated or not is easily reversible, so it's not too important to get it right.
When a page is set to "wikiOnly" then:
This can occasionally happen too though really for all tags it's ideal for there to be at least a sentence or two clarifying the intended usage, drawing attention to key resources, etc.