Engastration is a cooking technique in which the remains of one animal are stuffed into another animal. The method supposedly originated during the Middle Ages.[1] Among the dishes made using the method is turducken, which involves placing chicken meat within a duck carcass within a turkey.[2] Some foods created using engastration have stuffing between each layer.[3] The carcasses are normally deboned before being placed together.
The process is called engastration. That's not a very appetizing term for Thanksgiving, but an important one because basically what that means is that you're actually stuffing one animal inside the other. And that process actually probably dates back to the Middle Ages.