Music for Dummies from Dummies

I drove yesterday to the Ben & Jerry's factory with my friend TH. We were listening to the Radio and Avril Levigne came on. Earlier in the day, we had been talking about how she couldn't identify any of these songs on a mix, so I said, "Pop quiz, who sings this song?" Then we launched into a discussion of how to tell different types of music. So this is how we defined all of the following:

1) Alternative Rock: Can understand the lyrics, has guitar, base, drums
2) Rock: Can't understand the lyrics, guitar, base, drums
3) Emo Rock: high pitched, can't understand lyrics, guitar, drums
4) Emo: Slow, sometimes can understand lyrics, often only one accompanying instrument.
5) Ska: Lyrics come and go, guitar, horn.