Here's another bad one from earlier today. I could find dozens more by trawling through edit histories: one, two, three, four, five, etc. etc.
May I take this opportunity to remind everyone of some of the standard reasons for rejecting edits to tag wikis and excerpts:
This edit copies a significant amount of content from an external source. Generic descriptions such as encyclopedia articles and ad copy do not provide useful guidance; try creating something useful to this community specifically, and be sure to attribute the original author. See: How to reference material written by others.
lacks usage guidance
Simply defining what a [tag] is rarely helps those using it unless the tag's name itself is ambiguous. Excerpts should describe why and when a tag should be used.
circular tag definition
Tag excerpts amounting to, "[tag] is for questions about [tag]" are pointless and usually rejected. Excerpts should describe why and when a tag would be used.
(The last two of these are most relevant to the issue you raise, but I thought it was worth mentioning the first too, since that's often been an issue on similar sites such as SFF and M&TV, where people just copy information about a particular book or film verbatim from Wikipedia.)
Please also remember the advice which appears on the side of the screen whenever you're editing a tag wiki:
The usage guidance, or tag wiki excerpt, is a short blurb that describes when and why a tag should be used on this site specifically.
The full tag wiki is a detailed introduction to the topic, suitable as a destination for those curious about it:
► what questions should have this tag?
► some basic definitions
► brief introduction to the subject
► important links for learning more
► one reasonably sized page
See our advice on writing great tag wikis.
One important thing to take away from this is, as @Emrakul notes, that tag wikis and excerpts are two different things, and the guidelines for editing the two are different from each other.