In basic terms, a grill pan is a frying pan that has ribbed surface that allows food to cook with both direct contact and indirect heat. These handy kitchen utensils make grilling foods possible without a charcoal or electric grill. Grill pans made from cast iron can withstand high heats and can be placed both in the oven, or directly on an open fire (or on an actual grill).
There is another type of grill pan, which is technically not a pan, which allows for indoor grilling — electric grill pans. Also called indoor grills, these kitchen appliances can either be a single flat ribbed surface or two layers that fold over and cook food on both sides at the same time. Probably the most recognizable electric indoor grill pan is the George Foreman grill.