Choppa is a slang word often used by rappers to refer to their automatic weapons. The weapon mostly closely associated with this term is the AK47, but any automatic weapons can be called a choppa. In Lil Jay’s Competition song, he says “Team no lacking, so you know I got to keep the choppa”, he’s basically saying his team is always strapped hence you should know he has his weapon(choppa) on him.
Apart from being used to mean a gun, a choppa can also be used to refer to a helicopter/chopper. This term is from the movie “Predator” in which Arnold Schwarzenegger says “Get to the chopper”, but due to his heavy accent it came out as “Get to the choppa”, hence why some people started referring to helicopters as choppas.