A "FFL" is a Federal Firearm License.  There are currently over 58,000 FFL holders nationwide.  FFL holders are commonly gun stores, pawn shops, and retail sporting goods stores.  However, there are also many individuals that hold a FFL.  All firearms sold to individuals online must be shipped to a local FFL holder who will then transfer the firearm (via ATF form 4473 and associated background check) to the individual.