Pandora is an extremely-popular music streaming service that is available on a variety of platforms, including Android.
Taking the idea of a traditional radio service and bringing it to the internet, Pandora offers different tiers of service. It's primary revenue generator is its "free" service, which lets users listen to a set amount of hours per month of genre- or artist-based radio stations with audio ads interspersed every so often between tracks. For those who want to listen even more, Pandora One is the paid version of the service that removes advertisements, increases the audio quality, unlocks use of its desktop application and removes any limits to the amount of music you can listen to.
Because Pandora technically classifies itself as a "radio" provider and doesn't let users choose specific songs or albums to listen to, it negotiates lower per-play rates that it has to pay to artists. This has caused a bit of turbulence between Pandora, artists and music labels, but has also let Pandora charge far less for its service than other on-demand streaming music providers like Spotify, Rdio and Google Play Music All Access.
Pandora remains a great free radio option for those who don't take music too seriously and want to spend more time listening and less time managing playlists and searching for specific music.