The topic for the class was music and the one student who had shown up at that point asked the interesting question whether we say (or should say) boy band or boy group, and girl band or girl group. I was momentarily flummoxed, because I don’t usually talk about … whatever they are. Fortunately, there was a break immediately afterwards, so I did some quick research. It turns out that boy band is much more common than boy group, and girl group is more common than girl band. Among other things, Wikipedia’s relevant pages are titled boy band and girl group. Possibly the reason is simple alliteration. (Google Ngrams shows boy band from the 1860s. I wonder what kind those were then.)
There is a rock band from Ireland named Girl Band, who are all boys. On the other hand, there was Girlband, a pop group from Australia, who are all girls, and Girlband, a girl band from England, who are also all girls.
The question also arose about the difference between a group and a band. Both words can refer to any gathering of people, but band is more often associated with people who actually play instruments and group with people who sing and dance: compare rock band and pop group. (Google Ngrams shows that rock group was originally the preferred term, but that rock band took over as late as 1992.) There are also what Wikipedia calls all-female bands.
After two more students arrived, other questions were the difference between rock music and pop music, rap and hip-hop, Western music (that is, European/American) and western music (as in, “We got both kinds – we got country and western” (most often misquoted)) (the opposite would probably be Asian music rather than Eastern music), and “country music” (which one student took to mean “national music” – the music (or musics) particular to each country) and country music (as in, “We play both kinds …”). I said we didn’t really have to decide, which was a bit of a cop-out. Another difference which didn’t arise is classical, which in Europe means orchestras and choirs and in India means sitars and tablas.
PS 9 Feb: there’s also classical music as music which isn’t folk, jazz, pop and rock v Classical music (approx 1750-1825) v classic music or a classic, popular music v pop music, and (more specialised-ly) a sonata v sonata form.