During the short life of this SE, there have been several different lists of what is on and off-topic (which probably isn't unusual for a SE trying to find its identity). So this post is to make a canonical list of what is on-topic as of May 2016. Make each possible topic a separate answer, and upvote or downvote each one based on your own point of view.
Technical questions about music appreciation equipment (turntables, records, CDs, etc).
Questions about the history of a (named, identified) piece of music or a musical genre or musician(s)
Questions about recording technology which relate to a music fan's enjoyment of music, and are not too purely technical.
Questions about meaning or interpretation of lyrics of (named/identified) song.
Questions about the characteristics of specific musical genres.
Music-related questions that can be answered with some amount of objectivity, even if there isn't a single, provable, correct answer, and even if the questions generate some degree of opinion based on expert experience.
Examples of what I think qualifies here:
This answer is not intended to include questions entirely based on opinions, like:
Questions asking for help categorising a (named) piece of music, with identifying details
"Identify this song" or "identify this video" questions including specific details, such as identifiable lyrics, genre, time-period, instrumentation. A link should be provided if possible, but the description should also be contained in the text of the question.