"MG" is short for Maschinen Gewehr (translated: machine gun). "42" is for the year it was designed, 1942.

The MG42 was a multipurpose light machine gun designed by the Germans during WWII. It replaced the MG34 which was costly to manufacture and sensitive to fowling up in the mud. The MG42 was fast and cheap to manufacture, and they were produced in large numbers (estimates of no less than 400,000) by many companies including Grossfuss, Mauser-Werke, Gustloff-Werke, Steyr-Daimler-Puch. MG42 was rarely mounted on vehicles (this job was usually left to MG34s); instead its main use was by infantry. Usually it was used with its folding bipod. Ammunition was the 7.92x57mm cartridge (the same as was used in the standard rifles). It was belt-fed from either 50-round cone-shaped containers or 250-round boxes. Its rate of fire was 1200-1300 rpm, so the gun generated large amounts of heat. Extra barrels were carried along, and needed to be changed about every 200-300 rounds during sustained fire. The MG42’s tremendously high rate of fire gave it the nickname “Hitler’s zipper” for the sound it made. It was well-liked and well ahead of its time -- by far one of the best machine guns of World War II. Modified versions are still in use by NATO forces, and the U.S. M60 is also based on the MG42.

SPECIFICATIONS
Caliber: 7.92x57 mm Mauser
Weigth: 11.5 kg on bipod; 18 kg on light AA (anti-aircraft) tripod; 32 kg on infantry tripod
Length: 1220 mm
Length of barrel: 530 mm
Feeding: belt, 50 or 250 round
Rate of fire: 1200 - 1300 rounds/min
Muzzle velocity: 710 m/s

The MG-42 was a light machine-gun during World War 2, probably the most famous weapon of them all along with the M1 Garand. The MG-42 had a rate of fire at 1200 rounds per minute (RPM), yet, it couldn't fire such a bullet train, since the barrel will start to melt after a while. This machinegun was the choice of the German machine-gunner, since it causes panic amongst enemy soldiers when fired. It also makes a very distinctive sound, as it was called "Hitler's Buzzsaw".