If you buy a song (or album, we assume), you can share it with anyone you know that has a Google Music account, and...

If you buy a song (or album, we assume), you can share it with anyone you know that has a Google Music account, and they can then listen to that song for either a limited amount of time (maybe 24 hours) or a pre-determined number of times (eg, 5 playbacks).

Originally shared by Art Russ
http://www.androidpolice.com/2011/10/20/rumor-googles-music-store-will-not-have-subscriptions-but-it-will-have-song-sharing/