Frying pans are wide, shallow pans with a long handle and sloping sides.
The idea behind the slanted sides is to allow steam to escape so that frying and searing can happen. That being said, a frying pan can be used for sautéing or frying or steam frying, though not for deep-frying or stir-frying.
If what appears otherwise to be a frying pan has straight sides, then technically it’s classed as a sauté pan.
Frying pans come in varying widths. 20, 25 and 30 cm (8, 10 and 12 inches) seem to be the most common. The problem with wider 30 or 35 cm (12 or 14 inch) frying pans can be that burners on most home stoves aren’t wide enough to heat them evenly.
Very wide ones often have a small helper handle on the other side.
Frying pans are usually round, sometimes square. Occasionally, you’ll see square cast iron ones divided into compartments, oftentimes 1/2 plus 2 quarters. These are meant for bacon in one part, eggs in another, etc.
They can be made of stainless steel, aluminum, copper, anodised aluminium, cast aluminum, ceramic, silicone, pyrex, enamelled cast iron, or non-stick coated metal. Pans that are all metal (with metal handles, and no nonstick coating) can be used for baking in the oven. Cast iron also becomes a non-stick surface. Aluminum frying pans stick a great deal, but are often used for camping as they are very light to carry.
Some lighter-weight metal ones can warp, getting a slightly-raised dome in the middle of their bottom if they are used over heat that was too high for them.
Not all frying pans come with lids. If your frying pan doesn’t have a lid, but you want one for it, you can often find generic-sized ones sold at some stores (though they won’t necessarily match in colour and quality.)
Early frying pans would have either rounded or flat bottoms, because they would be used in hearths.
The advent of dedicated cooking stoves with flat cooking surfaces (called “dampers”) in the mid to late 1800s signalled the demise of rounded bottom frying pans.
Literature & Lore
“…but when he’s gone, me and them lonesome blues collide; the bed’s too big, the frying pan’s too wide…” — Joni Mitchell. “My Old Man”. 1971.
In French, a frying pan with straight sides is called a “sautoir”; one with with sloping sides is called a “sauteuse.”
“Frying pan” used to be the term predominantly used in New England; “skillet” was the term in the American south.