5 is a term used to describe your bro, it’s another way of saying “bro” or “twin” or “brother”. Not commonly used when saying a long sentence, usually only when saying something short
5 is Blood/UBN slang. It comes from the 5-point crown (People Nation) and is used as a sign of Blood affiliation or respect. Originally it was tied to the United Blood Nation, but today it’s used more generally as Blood lingo, even by sets like Sex Money Murda