A shotgun is a firearm. A revolver is a firearm. A pistol is a firearm. A rifle is a firearm.
If you want even more specific -- A Remington 1187 is a firearm (shotgun). A Smith and Wesson 686 is a firearm (revolver). A Sig Sauer P226 is a firearm (pistol). A Colt 6920 is a firearm (rifle).