Jamming refers to musicians playing together informally.
A jam session is an informal music event, process, or activity in which artists, usually instrumentalists, perform solo performances and vamp over tunes, drones, songs, and the continuation of songs.
It is the practice of recording an artist's song before that artist has had a chance to record his own version, as the Stanley Brothers did to Bill Monroe.
Thus, Option C is the correct choice.
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