What is a UMP/what does it stand for?

The UMP you are talking about refers to the H&K UMP. UMP is an acronym for the German name of the weapon: Universale Maschinenpistole. It is a light weight submachine gun chambered in 9mm luger, .40 S&W, and .45 ACP. It was developed in the 1990's, but didn't start m production until 1999.