A generic name for an earlyish firearm.
A longarm, usually smoothbore, muzzle loaded with black powder and a lead ball with a reliable 'accurate' range of about 50 yards. Had an F off calibre of .5 to .8 so when one of these hit you, odds for survival were pretty poor.
Initial form of ignition was a wheellock (a big spring rotating a rough surface against a piece of flint so causing sparks when the trigger was pulled). Very expensive, fragile and only really used by nob cavalry ... the peasants still used a lighted bit of string to fire theirs. arquebus.
Later method of generating the spark was a flintlock (flint held in jaws that could be pulled back and held till released by pulling the trigger). The Brown Bess being the classic British firearm of this type.
From about 1815 the percussion cap made it's first appearance. This replaced the flint and striker with a hammer and a small brass cap filled with fulmide of mercury (an unstable compound which explodes when struck). This speeded up ignition times significantly and meant that 'hang-fire'(where you pull the trigger but ignition takes a few seconds) was a thing of the past. Also meant that 'keeping your powder dry' was a bit less vital and rain wasn't as big a problem as it had been.
In the British Army percussion weapons didn't replace flintlocks til the 1840's, when they began converting the existing weapons to percussion. Percussion muskets were typified by the British P53 Enfield which was used extensively both in British Service and by both sides in the American Civil War