Pandora is an internet radio program. It streams music like all other internet radio stations. The difference is that the music that plays is based on the music you like. You enter the artist or song you like and based on that, it’ll suggest other artists and songs that you might like. It does a pretty good job in coming up with similar music to the ones you input. Pandora is based on the Music Genome project.
The founder wants to keep the interface very simple, so it is pretty easy to use. The design looks dated but it works. In addition to listening to the suggested music, you can also buy the music.