What is "deep cut"?
I came across this sentence today.

I was going to go for some deep cuts too, not just the stuff everyone knows.

In the original article, the word "deep cuts" was written in Italic.
This part was about music. I guess that it may be minor melodies or something in the music. Am I right? Is it a common word?

“The Success And Failure of the Super Mario Bros Opera”
https://medium.com/@songadaymann/a-brief-history-of-the-mario-opera-d99563e15b3c

Question

What is "deep cut"?
I came across this sentence today.

I was going to go for some deep cuts too, not just the stuff everyone knows.

In the original article, the word "deep cuts" was written in Italic. 
This part was about music. I guess that it may be minor melodies or something in the music. Am I right? Is it a common word?

“The Success And Failure of the Super Mario Bros Opera”
https://medium.com/@songadaymann/a-brief-history-of-the-mario-opera-d99563e15b3c

Answer

Thanks for the link. It really helped me in working out how to explain this exactly.

In music terms (recording artists), a "deep cut" is a track that doesn't get commercial airplay, and is generally ignored on an album. An obscure track (song/piece of music) in a musical artist's anthology.

We could have a guess at the meaning by looking at the end of the end of the sentence: "...not just the stuff everyone knows."

I guess the composer's plan is to "reward" the hardcore fans of the game by using the lesser-known pieces of music that only a hardcore player would know.