4L is a slang term in rap that comes from the phrase “for life.” It means “until death” or “for the rest of my life.” It is a simple contraction, simplification, or corruption of the aforementioned idiomatic expression. It can be used as:
Mark is set 4L after getting in Bitcoin early.
The term was and still is a prevalent slang amongst urban communities, especially those involved in rap. Young Nuddy, Pierre Bourne, and many more famous rappers have used this slang in their songs. 21 Savage would even title one of his rap songs “4L.”