Definition: A "percussion cap" is a small device that is used to ignite or explode something, usually in firearms. It works by creating a tiny explosion when it is hit or struck. This explosion then ignites the gunpowder in a gun, helping to fire a bullet.
In more advanced discussions, you might encounter the term in historical contexts, such as in discussions about the development of firearms or in military history.
While "percussion cap" has a specific meaning in the context of firearms, the word "percussion" can also refer to a type of musical instrument (like drums) that produces sound by being struck.