A Grill Pan is a frying pan with a solid bottom with ridges or grooves in it. The ridges allow fat to flow off the meat, just like it would drip between the grates of a grill, so a burger doesn't sit and boil in its own juices. They can also be flat cast iron or cast aluminum pans, with low sides and a raised lip around the edges to prevent drips and spills. Grill pans fit over single or double burners. Some double burner grill pans also have a griddle (no ridges) on the reverse side and offer more surface area for cooking.