I've seen this couple of times—people copy information from Wikipedia or somewhere else, and paste it into the tag wiki/excerpt as is. This is not how it was meant to be used! You can't just dump some piece of information, however accurate it may be, without spending any effort racking your brain thinking what that tag/topic means for Unix & Linux, this site.
The tag excerpt is the elevator pitch for the tag. It should explain what the topics to be tagged with this tag are. If it doesn't include how-to-use-it, it's likely a bad tag excerpt.
The tag wiki is more extensive. Apart of being more verbose about it's usage, it can contain some basic terms, references, etc. If you just dump the entire wikipedia article it's very likely that it will be rejected.
To reviewers: please, read these edits carefully. These are informative bits of the system usage, and it's very important that it's accurate. Evaluate them all with extreme prejudice and do a search of phrases on the Internet to search for plagiarism. If you see a tag wiki/excerpt that's too good to be true, it is likely plagiarism.