DA means district attorney. The relevance of this and urban terminology is it's connection with punishment for crimes. If you get caught by the 'Po (police for yall) selling drugs or whatnot, you
will probably have to deal with a District Attorney. District Attorneys only practice law in district courts (imagine that). If you
murder someone or get caught with enough
coke to make a state, or even worse, a federal
case, you won't be dealing with a DA, you'll be fucking with a whole new ballpark of lawyers and attorneys.