While at first glance, what we mean by 'popular music' might seem to be quite straightforward and self-explanatory (it's music that's popular, right?), there has been considerable discussion in academic circles about what actually constitutes 'popular music'.
Here are a few different ways that the term might be defined (but not all of them...) and some of the problems with these definitions:
* music that 'lots of people' like (in the sense of 'populist' music which appeals to a critical mass of people -- but we might wonder, how many people need to like it before it is deemed 'popular'?)
* music that is 'of the people' or produced 'by the people' (ie, 'popular' in the sense contained in the Latin root of 'popular', popularis, which means 'of the people') -- so this refers to genres that emerge at a grass-roots level in community settings, like folk music, but also to other everyday practices like singing in the shower, mass renditions of the national anthem, karaoke, and so on. But who are 'the people' in this case, and does that make pretty much everything 'popular music', or does it actually exempt music that comes from the commercial recording industry (like Top 40)?
* music that is not classical music, or not 'art music', or otherwise apparently 'elite music' -- but where does this leave well-loved and widely-used pieces of the classical repertoire, like Pachelbel's Canon or Orff's O Fortuna? And what about the the super-stars of classical music, like Andre Rieu, Nigel Kennedy and Vanessa-Mae, who have blockbuster albums and tours to rival the big international stars from the world of pop and rock?
* music that is produced and distributed by the recording industry, so is a mass-mediated commodity that is part of the cycle of capitalism -- but does that mean that music that is not produced in this way (for example, self-released albums, or home recordings distributed on the internet), that might otherwise fits into the genres of rock or reggae or punk or hip hop cannot be called 'popular music'?
And that's all before we start a debate about what counts as 'music'!
As you can see, the seemingly basic term, 'popular music', opens up a confusing area -- at least for academics. There's a wonderful article in a 2005 edition of the academic journal, Popular Music, in which some of the leading writers in the field tie themselves into knots trying to define what 'popular music' actually refers to (see Popular Music vol. 24, no. 1, pp. 133-145). Some of this debate also belongs to a longer set of discussions in the study of popular culture. If you're interested, track down the influential article by Stuart Hall, 'Notes on Deconstructing "the Popular"' (still one of my favourite pieces in the field -- find it in R. Samuel (ed.) (1981), People's History and Socialist Theory, Routledge & Kegan Paul, London, pp. 227-239).
At the end of the day, though, and for our project, we're happy to think about popular music in its broadest possible sense, to incorporate all of these definitions and more. We're not so interested in these debates as we are in how music, in all its forms, finds a place in people's understandings of and connections to the past, and how we continue to find traces of music from the past in our experience of the present.