According to the ATF, A firearm designed fire more than one bullet with a single pull of the trigger. They are highly regulated and require a lot of expensive bureacratic paperwork and a squeaky-clean record to acquire the Class III Federal Firearms License needed to legally own one. The M-16A2 would technically fall under this category because of its ability to fire in 3-round bursts.

AR-15s, civilian semiauto AK-47 clones, etc, ARE NOT MACHINE GUNS. The most common AK-47 variant in the US civilian market is the Romanian-built WASR-10, imported by Century Arms, because it is the least expensive AK. Although similar in appearance, they DO NOT fit the definition of MACHINE GUN because they fire one and only one round with a single pull of the trigger, which means they are semi-automatic. An AR-15, despite its similarity to an M-16, is not the same thing. Vietnam-era M-16s were true MACHINE GUNS also, capable of fully automatic fire. The Pentagon brass found this to be a waste of ammo and restricted later models to 3 round burst mode as the only option for selective fire.
Machine guns are mainly carried by the military and only rarely found in civilian hands.

The belt-fed American M-60 machine gun is based on an earlier German model from World War 2.

Most ordinary Americans can't tell the f*cking difference between a real machine gun and a semiautomatic like the WASR-10 or AR-15. Unfortunately the News media and politicians are similarly misinformed, to the detriment of all.
by JJRtwu2008 March 20, 2008
Get the machine gun mug.
An amazing song written by Jimi Hendrix to protest the Vietnam War.
Machine gun, tearing my body all apart
by Hydroman1071 August 25, 2006
Get the machine gun mug.
When a guy gets a BJ from a random woman and pulls out, nuts on her face, and screams RAT-TATTA-TATTA
Friend: Hey man what did you do to her last night?
You: Oh I just gave her The Machine Gun all over her face
by MistxLobsters August 3, 2017
Get the The Machine Gun mug.
a type of weapon. machine guns first appeared in world war I and revolutionized warfare, leading to the invention of tanks. machine guns are subdivided into light machine guns and heavy machine guns (the former can be used and carried by a single person while the latter is mounted and has to be used by a crew).
machine guns enabled a single soldier to kill a whole group of other songles in a few seconds.
by Awesome McAwesome October 13, 2007
Get the machine gun mug.
An automatic (rapidfire) weapon first developed in the late 19th century. The recoil from the first bullet fired resets the mechanism to fire again. The next bullet is pushed into the barrel from the magazine - either by gravity (as in early weapons) or a tensed spring. Revolutionised warfare by making it notoriously easy to mow down large numbers of attacking infantry at decent range, was very handy when conquering spear-armed peoples. Went on to a much longer and bloodier history as the design was refined.

Comes in a variety of calibres, weights and rates of fire, from sub-machine guns (use pistol bullets to reduce size and weight) to light machine guns (use assault rifle bullets for compatability and to reduce size and weight) and heavy machine guns (sheer firepower, no compromises).

SMGs and LMGs are meant to be carried. Anything larger, and you're doing a Rambo.
The M2 machine gun, the original and the best. Used by the US from WWII right through to now. Ever wondered why the MGs on the top of Sherman and Abrams tanks look so similar? They're M2s.
by MAI742 October 24, 2009
Get the machine gun mug.
Putting your index finger in someones anus

while keeping your thumb up and your other fingers retracted, thus acting as if your hand were a gun, while moving your finger back and forth fast and making machine gun sounds.
You would'nt believe how much this girl enjoys me machine gunning her asshole!
by DVESenS March 10, 2012
Get the Machine Gunning mug.