Our tag wikis are best when they have informative descriptions and excerpts.
However, we have a low-grade but ongoing problem with copyrighted material being copied and pasted into our tag wikis. Often these are suggested edits, yet the problem isn't being caught in the review queues.
The short version
Don't just copy text into our tag wikis from elsewhere. It's almost never legal to so, even OGL or Wikipedia text. (It's possible to cite OGL or Wikipedia text legally, but it's very difficult to do it correctly. If in doubt, just don't.)
When in the Suggested Edits review queue, check unusually nice suggested edits in a search engine to see if they were copied, and reject them if so. Be a bit more suspicious, a bit more alert for the natural human tendency to be “helpful” by taking the path of least resistance and just copying text from elsewhere.
The long version
I just rejected two suggested edits to a tag's wiki, and rolled back four other tag wiki edits that had passed the suggested edit review queue. The first two used unattributed OGL text and the others used unattributed text from wikis.
Not naming any names because this stuff is legitimately not obvious, and no harm was done anyway in this case. It's a trend that's been developing over a long time, and these were just the most recent examples that tipped me toward addressing it explicitly. Things are pretty good actually — but we can always do better and better is awesome.
OGL material and wikis (like Wikipedia) are copyrighted
It's counterintuitive, I know, but both OGLed text and Wikipedia text are copyrighted works. The only way anyone is allowed to copy and reuse their text is by following their respective licenses. They cannot be freely copied from the way that has been happening in our tag wikis.
The problem is that both of them require specific types of attribution in order for their reuse to be legal, because their licenses say so, but the design of tag wikis makes proper attribution difficult or even impossible to include.
Our tag excerpts are just plain too small to contain attribution. It's impossible to use open-licensed material that requires attribution in our tag wiki excerpts. New tag wiki excerpts must always be original writing from the person making the edit.
This is a bit more complicated in our tag wiki descriptions themselves, because there we do have a bit more room.
Wikipedia and other wikis
Attribution for Wikipedia articles is small enough to include in the full tag wiki description, so it's technically possible to reuse the Wikipedia text in our tag wiki descriptions. If attribution is included, Wikipedia text may be reused in our tag wiki descriptions.
To use Wikipedia text, refer to their citation guidelines available by clicking “Cite this page” in the sidebar of a given article. The guidance page looks like this. If figuring out how to write the attribution from the information on that page seems intimidating and confusing, that's a good sign that one isn't equipped to reuse text from Wikipedia on a public site like RPG.se.
(You might see now why I rolled back those edits instead of attempting to add correct attribution, despite having a lot of experience writing Creative Commons license attributions. ;)
Tag excerpts still need to be freshly-written, original text when using Wikipedia text in the larger tag wiki description.
All this goes for wikis other than Wikipedia too, except they usually don't have even a confusing page about how to cite.
Open Game License material
The Open Game License (OGL) also allows reuse of text, but to do so requires including a verbatim copy of the entire license along with the text, as well requiring specific edits to be made to the included copy of the license.
We obviously can't put a copy of the entire OGL in the tag wiki excerpts. We could, in theory, past a copy of the 1,000-word OGL into each and every tag wiki description that uses OGLed text and update it in the way that it requires, but that's ridiculous — it's easier and saner to avoid copying and just write in our own words.
And even if we did, the tag wiki excerpts still wouldn't be covered by the license, because they routinely appear elsewhere on the site alone and the OGL doesn't allow that.
There are very few exceptions that work with the constraints of our tag wikis.
There are licenses which don't require attribution; these are rarely used for text though, and I've never personally seen RPG descriptions or reviews released under such a license.
Some people release their text into the Public Domain, which means it can be reused with no attribution at all, and for any purpose. In practice, this is even rarer.
In general, if text appears elsewhere on the internet that matches one of our tag wikis, it has been improperly added to our tag wikis.
What to do
When submitting a tag wiki edit, either avoid copying text, or commit to learning how to write correct license attributions.
When reviewing suggested tag wiki edits, test any unusually well-written text by plugging a sentence or two of it into a search engine. See if an SRD or Wikipedia or another (normal, non-open copyright) site comes up. If so, reject the edit as harmful, with a note that Wikipedia/OGL/copyrighted text cannot be used without a license.
Alternatively, if you're feeling flush with time and know what you're doing, click Improve Edit and add an attribution to the appropriate part of the tag wiki description, according to the text's license.
But… Fair Use / Fair Dealing?!
It's often unclear whether a case of text copying would be protected by fair use/dealing doctrine. There are arguments that could be made for and against tag wikis being covered by the doctrine. Copying that isn't a 100% crystal-clear case of fair use/dealing is best considered not, and avoided.
Since we have no need to copy text for our tag wikis, it's both unnecessary to tread in grey areas of fair use/dealing, and that lack of need may actually be a strong indication that it's not a protected form of copying anyway.