Q. is a short written form of the word question. You see it in quizzes, worksheets, and notes: Q.1, Q.2, or Q. before the question and A. before the answer. People also say a Q and A (or Q&A) for a time when the audience asks questions and someone answers them — after a talk, on a show, on a webpage. You almost never say 'Q-dot' out loud; you either read it as question or, in Q&A, as the letter names. Though actually, a capital Q by itself can mean many other things — a letter, a name, a grade — so this meaning lives in the pair Q. / A., or in Q&A. Older British writing likes the full stop after Q; a lot of people now just write Q.