The Musket is a type of; usually smoothbore, usually large-caliber, long gun that is muzzle-loaded, shouldered, then fired. This firearm developed in 16th-century Spain. It is a type of long gun that was used by soldiers before the invention of the rifle.
Musketeers were nothing more than soldiers armed with black powder muzzle-loaded muskets practicing the drill of musketry. Musketry is the use of small arms in battle, small arms refers directly to muskets.
The musket was quite a versatile firearm as it had the capability to shoot a single lead round ball projectile with reasonable accuracy to about 50 yards yet powerful enough to reach several hundred yards, or it could be loaded with many smaller projectiles or lead shot to harvest small animals and birds for food.
The musket has quite a history as it first appeared with the use of the matchlock ignition system and would see use of other improved ignition systems up too and including the percussion lock. At this point in history the musket would evolve into two very distinct firearms: the addition of rifling it evolved into a rifle with the addition of a two piece sighting system for shooting accurately at long distance, smoothbore and choke-bored it evolved into a shotgun with the addition of single front bead sight for quick target acquisition or short range pointability.
A musket has a smooth bore, a rifle has a rifled bore. During the transition period between smooth bore Muskets and then the addition of rifling to the bore of muskets, these firearms were commonly, then, referred to as "Rifled Muskets". Standard military nomenclature of the period between 1820 and 1860, refered to Springfields, Enfields, etc, as "Rifled Muskets".