A subject of some argument: loud, ongoing, and opinionated argument, at that.
The easy answer is that filk is science fiction folk music—which may explain nothing! The slightly more complicated answer is that it’s music based on themes of science fiction, fantasy, and fandom… or on the space program, modern technology, computers, cats, food, TV shows, movies, robots, fairy tales, mythology, classic literature, folk tales, sailors’ legends, poetry, fiction as a concept, or just about any other subject people in SFF fandom like to talk about.
The even deeper answer is that filk is the music of the filk community, regardless of what the songs are about. If you’re a filker and want to share your songs in a filk circle, it’s filk, no matter what it is.
Historically, it’s a primarily folk-based genre. Most filk music is played on acoustic instruments, and the lyrics make up a significant aspect of the song. But filk as a genre is always expanding, and it can sound like anything from traditional Celtic folk to pop music to rock to hip hop, and beyond. Unsurprisingly, popular music is a strong influence on the genre, and many filkers (even original songwriters) engage in the occasional parody to the tune of a popular hit.
In Southern Ontario the quality of filk is pretty high, and we’re proud of our little community, the United Filkers of Ontario (or UFO). If you’re going to be in the Greater Toronto Area, we’d love for you to join us!
For more extensive discussion, check out Interfilk’s What is Filk? page. There’s also lots of information on what to expect from a filk convention on our For First-Timers page, as well.