A gridiron is a metal grill used for cooking food over a fire. Don't throw your burgers on your friend's gridiron if she's a strict vegetarian!
Just as the word implies, a gridiron is a grid, or two crossed sets of parallel bars, made of iron (or another kind of metal). In addition to cooking gridirons, there are also gridirons that support heavy equipment on film sets. In sports, gridiron is another name for an American football field, marked off in grid-like yard lines. Gridiron shares a Latin root with griddle.