Google Music Discovery was both a feature of Google search and a separate service. When you searched for a song, lyrics, or a performer, the search results included the ability to play songs from available partner databases.
Most of the features of Google Music Discovery were rolled into Google's beta product, Google Music. Google Music Discovery originally included a large number of partner services, one of which, Lala, was purchased and then dismantled by Apple. Other music partnerships remain, and users can sample and discover new music through Google Music. Google Music is in invitation-only beta as of May 2011.