What does "K-On!" refer to in the series? I have been watching the English dub of it on public TV and I haven't seen any mention of K-On in the series itself (with the exception of the OPs/EDs).

So I am wondering, what does K-On refer to in the series? If it refers to nothing, then is there a particular reason/meaning to the name K-On?
"K-On" is pronounced the same as the word 軽音 keion, which means "light music" (in the Japanese sense, not the classical sense). The main characters are, of course, part of the light music club, which is the 軽音部 keion-bu. The "K-On club", if you will.

If you had watched it with Japanese audio, you would have probably noticed the word sprinkled all over the place (since they talk about the club a lot, obviously). The eyecatches (I forget for which season) also have audio of Yui saying "K-On". I suppose they must have changed the eyecatches to something else for the English dub.