Holster makers seem to differentiate a "blocked" holster from a "boned" holster by saying a "blocked" holster is shaped around a pistol form and may not get the fine detail that "boning" gives a holster. My understanding is that "boning" means to take a hard smooth piece of material (originally made from bone, probably some kind of plastic now) and use it to very finely crease and form the leather around the features of the gun, whereas "blocking" will not conform the holster to the pistol as closely.