Nice piece at Wired about tagging music collections:
To compensate, programmers invented tags, which are pieces of text and graphics that live in the MP3 file and can be parsed by most jukebox players. Tags that are complete and well-organized make it possible to find the perfect song to fit the mood of your intimate dinner party or Dionysian rager. Anything short of that and your guests will long have departed by the time you’ve located the tune. Soon enough, my hobby as a music collector morphed into one of a librarian.