This category merges together Light Machine Guns and some Directed Energy Weapons to make one category known as the Heavy Weapons, which consist of low mobility weapons that have large/infinite amounts of ammunition at their disposal.
These weapons are available as Payloads for the multiplayer's Combat Rigs. In campaign, the Steel Dragon, Eraser, and Ballista EM3 are selectable from the Heavies slot of secondary weapons (during gameplay, they are also referred to as "Heavy Weapons").
The MDL in Call of Duty: Advanced Warfare was originally bought from the Heavy Weapon category in Exo Survival, but after an update, Launchers were added to Exo Survival and the MDL was moved to this category.