The usage of the tag itself needs to be defined.
As listed in Rand's answer, a wiki excerpt needs to provide the usage for that specific tag. Although a short description is usually good, it should not drown out from the usage. The usage is essential here. To round off the tag, suggesting guidance for how to use sub-tags (assuming it's not a universe tag).
A good example is our current tolkiens-legendarium tag wiki excerpt written by Rand'al-thor
For questions about any works in J.R.R. Tolkien's Legendarium - The Lord of the Rings, The Hobbit, The Silmarillion, and other works set in the same universe - or about that universe as a whole. Questions about movies, games, or other media set in the same universe should also use this tag. Questions about Tolkien himself or works by him which are not part of the Middle-earth universe should NOT use this tag.
Tolkien's Legendarium tag wiki excerpt and info
The reasons (and subsequent discussion) for my rejected edit can be found here
A well known children's book series featuring the lovable bear Winnie the Pooh, his various companions in the Hundred Acre Woods, and their human friend, Christopher Robin.
That isn't tag usage, that's a tag wiki
Initial reasons for rejection: 1 and 2
Above are listed my initial reasons for rejecting the tag. For the majority of the excerpt, it's a wiki, the rest is (less-than-accurate) guidance for how to use another tag.
I go on to describe, after a moderator asks what usage is required, the usage requirement for a tag wiki excerpt:
Rand al'Thor: What usage guidance does this tag need?
Edlothiad: When to use the tag.
Short and sweet, your tag wiki edit, provides no usage for how to use the tag itself, it merely gives a description of a set of books, which feature a set of characters. Although these book are directly related to the tag, they're not telling us when to use them.
"But Ed, why would we need to give a guidance for the tag if it's obvious?" - Confused User
Well, Confused User, as laid out in this comment:
your point is entirely moot, because if that was the case, what is the point of a tag wiki excerpt? The edit did not make it clear how we should be using the tag, and also held incorrect usage information for the Disney tag. The new tag wiki excerpt is much clearer, and without tooting my own horn, a good example of how excerpts should be laid out.
A wiki-excerpt is useless if we assume "the usage is obvious". The excerpt is for laying out the specific usage of that tag, stating when to use it, how to use it, where to use it, and only in addition to those, what to use it with (back to that later).
A stander-by then makes a good point about some crucial guidance the tag wiki excerpt is missing, the when, how and where (all three are, in essence, the same).
Mithrandir: I think that this tag wiki should specify that it's about the books and the movies and the TV shows etc
Finally, the "what to use it with". This one is more tricky and sometimes requires some research effort. One has to familiarise themselves significantly with the tags in question, the questions that have been tagged with those tags and whether they have been tagged by the OP or added later. This is particularly difficult for Disney questions, as although 46/61 questions are tagged exclusively to Disney's works involving their fairy tales (e.g. Disney's Frozen, Disney's Brave etc.) 15 of the question were tagged with (mostly story-id and Star wars) tags which seemed for the most part odd.
In this case, given the fact Disney's Winnie the Pooh is only one adaptation of the work, it would not make sense to add the Disney tag to all the questions about Winnie. winnie-the-pooh should be its own universe tag, and should not be scoped within Disney due to the multitude of works outside of the Disney scope.