Spatchcock is a cooking technique. It means to split open poultry and grill it.
You use sturdy kitchen shears, and make two cuts in the bird, one along each side of the backbone to get at it for removal. Then you turn the bird over and press it open and flat. This allows the bird to be cooked quickly and evenly. In the past, the bird may have been partially deboned in addition to the backbone.
Spatchcocking a bird is a popular way of preparing chicken for the barbeque in Australia.
The term has also been seen applied to lamb.
Though you might be tempted to use the word “butterflied”, “butterflied” is generally applied to boneless pieces of meat.
Not the same as Spitchcock.
No one is certain where either part of the verb actually comes from. One guess is that “spatch” is a corruption of “spitch”, which in turn is a corruption of “spit.” It’s conceivable that the grilling or roasting may have been done with the bird impaled on a spit. The “cock” part at the end almost certainly comes from an older form of the word “cook” (viz. the German word, “kochen”.)
Another theory is that it comes from “dispatch cock”, as a fast way of cooking a bird. But then, grilling it wouldn’t have been a special way of cooking birds, with pretty much the only other method available being boiling.
The French word for this is “poulet en crapaudine” (chicken served toad-style. Some in English call it “frogging” the chicken.
The word can also be applied outside the kitchen to someone’s forced introduction of one topic into another.