I regularly see the abbreviation
OP used in comments and in questions on the meta site. What does it mean?
Should a glossary be included in the FAQ? Or should
OP be included in an existing glossary I do not know of?
OP means Original Poster, in other words, the user that asked the question.
OP is a term commonly used all over the English speaking Internet, in forums, bug reports and social news sharing sites.
I do not think it should be included in the FAQ, as it is a fairly common term. People who are unfamiliar with it can look up this question or search for it on Google. It's listed in Wikitonary and other online dictionaries.
I agree with Flimm that OP doesn't need to be the FAQ. But I do think it should be in the glossary.
And it is in the glossary! It's somewhat confusingly under "Ask Ubuntu/Stack network specific terms" (even though it's not really specific to SE or AU).
The entry for it says:
Also, people should feel free to ask us what that and any other jargon means (as well as to search for or look up the term, as Flimm suggested).