Light Machine Guns (or LMGs for short) are a class of small arms designed to offer short bursts of automatic fire in direct support of infantry operations. They are principally designed to be used from a bipod and typically also able to be fired from the hip or shoulder.
Light machine guns can be belt fed but more typically use a magazine: they can fire full-sized rifle rounds, but most modern examples use intermediate rounds. Many modern examples are simply assault rifles with larger magazines and heavy barrels to prevent overheating.
Some of the earliest developments in light machine gun technology were weapons intended to be used by horse cavalry units, in order to compensate for the lowered accuracy inherent to riding a moving horse. However, they soon found a role in infantry operations, granting suppressing fire capabilities to infantry units that were still mostly armed with bolt-action rifles and greatly improving the firepower of the squad as a whole. In these early days, they were often referred to as "automatic muskets" or "machine rifles."
In World War 2, Germany attempted to develop a "universal machine gun" (what is today called a general purpose machine gun) which would be able to perform the roles of both light and medium machine gun, depending on whether it was issued with a bipod and belt box or a tripod and long loose belts. While the resulting MG 42 was a superb suppression weapon, it was somewhat poorly suited to the LMG role, and postwar developments saw the adoption of a new wave of light machine guns using the intermediate cartridge concept to compliment the heavier GPMGs.