It's a dog, usually owned by a bit of a fop, who freezes in quivering fear at the scent of a bird, then watches in horror and amazement as the master who feeds and shelters it walks in front of its cone of terror and kicks at brush and grass clumps until a bird lifts from the ground, then shoots twice at it and sometimes kills it. These bird dogs will then sometimes run to a bird and begin to mangle and chew at it, again, obviously out of fear. Their fop owners will call this, hilariously, a "good retrieve", as they smooth out whatever is left of the clump of feathers they have just pried from their dogs jaws. Other times these "bird dogs" will watch, again I assume, in terror, as their owners walk around trying, often in vain, to find the birds they just "harvested". The fop will often say ridiculous things about their dogs ridiculous behavior like "slammed on point" or "staunch" or bloviate about "good dog work" or - and I'm not exaggerating here - "style". Generally the cowardly animal will have between 3 and six collars on it, often with antennae and other such digital over compensatory phallic substitutes. These "bid dogs" generally be ugly, often there is an attempt by breeders to disguise the dogs' ugliness by covering it in excess hair, though occasionally these disgusting creatures are displayed nearly bald.
This is opposed to a gun dog, or a duck dawg, or, highest praise of all canine epithets...a "hunting dog".