1 - a simultaneous or continuous discharge of firearms
2 - a general discharge or outpouring of anything
3 - to attack or shoot by a fusillade
Origin French, 1801, from fusiller (to shoot) and fusil (musket)
In the context of military tactics, the term is generally used to refer to a type of organized and concentrated gunfire from a military unit armed with small arms, and initiated by a command from a commanding officer.