I've been going through recent edit suggestions, and I noticed that a few users are being dedicated in their tag curation. That's fantastic; thank you. However, I've also noticed that some content is taken word-for-word from outside sources (sometimes Wikipedia, sometimes other sites), often without attribution. That's plagiarism, plain and simple.
It's also true that copying-and-pasting content from elsewhere is usually not the best course of action - even with attribution. There are better ways to summarize relevant information in a tag wiki, and they don't involve copying someone else's work. In fact, there's a Reject option for tag wiki suggested edits for this reason:
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.
See also What is a tag wiki? How do I write a good one?.
Please don't plagiarize. It doesn't help the site.