Patch, often colorful, of bare skin on the throat that may be distensible or inflatable (as in Magnificent Frigatebird).
Loose area of skin extending from throat as in pelicans and hornbills
Or gular sac is located below the lower mandible, that allows some birds to hold their food.
also called the Gular Sac, a skin pouch of the throat found in some species, most obvious in the pelicans. Less conspicuous gular sacs are found in cormorants, owls, pheasants and pigeons. 
A loose and pronounced area of skin extending from the throat (e.g. on pelicans or hornbills).