Simply the cooking grids are the primary surface of BBQ grill where you put your food for grilling and are located directly above the rock grates or heat plates.

They are commonly called:-

Cooking grids/Cooking grates/ Cooking grills that’s  depending on the manufacturer.

Porcelain Cast Iron Cooking Grids

Cooking grids can be made of many materials but  most common are stainless steel, porcelain-coated cast iron and porcelain-coated steel.

Stainless Steel Cooking Grid