FFL (Federal Firearms License)
A federal license that authorizes a person or business to engage in the firearms business — and the dealer who processes transfers.
A Federal Firearms License is issued by the ATF and allows the holder to manufacture, import, or deal in firearms. In everyday use, 'an FFL' usually means a licensed dealer. When you buy a gun online or across state lines, it must ship to an FFL near you, who runs the background check and completes the transfer (often for a small fee).
FFLs are central to lawful transfers: they maintain records, run the NICS background check, and ensure the buyer is legally eligible. Different license 'types' cover different activities — a Type 01 is a common dealer, while Type 07 covers manufacturing. If you're transferring a gun to someone in another state, federal law requires it go through an FFL.