It always happens that user populate a tag with content plagiarized from Wikipedia.
What should we do about this or any other plagiarism?
While it is permitted to copy content from Wikipedia with proper attribution (which is impossible to do in the tag excerpt) it is a bad idea in general. Tags are intended to describe how the tag is used on our site. Definitions on Wikipedia are often too complicated or simply not useful in our tagging system.
If users need the description provided by Wikipedia… they could check Wikipedia.
There are two problems I have noticed that make controlling this problem hard. There is no edit history on tags and simply deleting the content submitting an empty tag isn't possible. I encourage proof-readers of tag wiki edits always to check for plagiarisms.
In general, while this is technically attributed with the "WP", it isn't very good form - the whole point of tag wikis and tag excerpts is for people to know what the tags are for without having to seek out another site.
In general, things need to be attributed correctly, and outright plagiarism is never a good thing. We also want the exerpts and the wikis to be relatively short, so that the user can find out what they need without having to go anywhere else or spend a lot of time struggling with what the tag means, and often wikipedia content is just too much unnecessary information for tag wikis if it isn't selected carefully.
In general, people are more than welcome to source content from other places if they really find they cannot word it well on their own, but it must be attributed, and generally using your own words is preferable to a straight copy and paste, even if it is attributed.