The following information is regarding TuneCore's Publishing Administration service
A composition is a musical work, with or without lyrics, that has been created by a songwriter/composer.
A sound recording, often also referred to as a "master”, is the recording of a performance of the underlying composition. This includes beats, percussion, bass, guitar, vocals, etc.
For example, Dolly Parton wrote the composition (meaning she wrote the lyrics and melody), to "I Will Always Love You." Arista Records recording artist Whitney Houston recorded a version of Dolly Parton's composition. In this case, Arista Records owns the sound recording of the song while Dolly Parton and her publisher own the composition.