Carry over cooking

Carry over cooking refers to the phenomenon that food retains heat and continues to cook even after being removed from the source of heat. The larger and denser the object being heated the greater the amount of carry over cooking. After being removed from the heat source (oven, barbecue grill, etc.) the internal temperature can continue to increase. This means that when cooking large roasts or turkeys, for instance, the roast meat should be rested before serving to allow heat to distribute from the warmer outside to the cooler middle, also allowing juices to distribute throughout the meat.

Physics

As mentioned above, the larger and denser the object being cooked, the greater the degree of carry over cooking. In more scientific terms, larger objects have a lower surface area to volume ratio and thus retain heat better. Denser foods typically have more water content. Water has a higher heat capacity and thus there is more heat in the food object to continue the cooking.