Much the same as a boot polisher, used most often when south of Kentucky.
It takes a well-trained pup to work up a good spit shine on a pair of brogans....once found, one such pup is valued accordingly.
It's when you trip over the dog in any cover. Most people see it as a derogatory term, after all if the dog doesn't get farther than where you can stride, you will find as many birds as he does! But, the good news, even if they wild flush you get good shots, and you can retrieve easily! Open bored guns with polywad spreader loads, please. Also, it's like a rattle snake when you see a boot licker, after you collect your wits, from the trip and fall.... you know! Shall we get a definition to "fire breathing dragons", "egg sucking hounds" , (usually retrieves but eats the bird) "over the hill", ( kind of like a firebreathing dragon, but busts the birds).
A good dog in early ruffled grouse season. Otherwise, not too useful. Had a dog that as a pup that did this, but, as she got older she ranged farther. Became the best dog I ever had.