MP40 was a subgun. Full name Maschinenpistole 40. 40 being it's year of adoption. Commonly called the "Schmeisser" by American GIs after a German weapons designer Hugo Schmeisser.
The MG42 (Maschinengewehr 42) is the belt fed crew served full machinegun which is similar in many ways to an American M60. It was a very scary gun due to the sound of it's extremely high rate of fire.