A compilation album is an album (music or spoken-word) featuring tracks from one or multiple recording artists, often culled from a variety of sources (such as studio albums, live albums, singles, demos and outtakes.) The tracks are usually collected according to a common characteristic, such as popularity, source or subject matter. When the tracks are all essentially by the same recording artist, a compilation album is often referred to as a retrospective album. Compilation album may employ tradition product bundling strategies.