Noun
(music) An obscure song by a well known musician.
"Dig a Pony" is my favorite Beatles deep cut.
(idiomatic) Any obscure work, a thing likely to be recognized only by a connoisseur.
I'm a fan of Kurosawa's films, but The Bad Sleep Well is a bit of a deep cut.
Used other than figuratively or idiomatically: see deep, cut.
Source: en.wiktionary.org