Name of the M249 SAW (Squad Automatic Weapon) deveoloped by Fabrique Nationalie.
Also named SAW as it wasdeveloped as part of the Squad Automatic Weapon project to find a suitable light machinegun for use in infantry teams.
The prototype designation was XM-249. The M249 is used by US troops mainly, but is also replacing the SA80LSW as the british infantry light support weapon.
Called largly teh SAW by US troops and Minimi by UK troops.
"Get that Minimi set up on the 3rd floor, east side, that way you can get good field of fire on the square"
"Yes sir, 249, east side, 3rd floor, overlooking the square"
Also used by the Canadian Forces as a squad support weapon and designated the C9.
"I need two C9s in the tower"
The other two definitions are correct, but omit the origin of the term. It was originally "mini-mittreilleuse" (not sure of spelling on that), a French neologism meaning "small machinegun". It's a 5.56mm weapon that fires the same NATO standard rifle ammo as the M16. It is normally fed from 200-rd belts, but can also accept 30-rd M16 magazines.
The Minimi is not a popular weapon because it is prone to malfunctions and the 5.56mm projectiles don't penetrate much in an urban environment.