It’s a combination of votes and one person’s opinion about a great riff or lyric or whatever, but not the whole song. I didn’t agree with some selections, and given a year or so to think about it I could probably do better. None the less, there’s a lot of really cool stuff listed at The 50 Coolest Song Parts.
I looked at all 50 and listened to about half to make sure I knew exactly which part they were referring to. And because I wanted to hear them again.