What baking tray means
A baking tray is a flat, rectangular sheet of metal used in the oven. It may have a low rim around all its edges, which keeps juices and oil in place, or it may be completely flat or have a raised lip along only some sides, which makes it easy to slide biscuits or pastries off. In Britain it is also called a baking sheet or oven tray, while in the US it is called a baking sheet, sheet pan or cookie sheet. Baking trays are among the most useful pieces of kitchen equipment.
They are used for baking biscuits, cookies, scones, bread rolls, free-form loaves, meringues and pastries, for roasting vegetables, potatoes and chicken pieces, for toasting nuts and seeds and for making tray bakes, where a whole meal is cooked together. Trays are made from aluminium, steel or carbon steel, often with a non-stick coating. Heavy, thick trays are less likely to warp in a hot oven and heat more evenly. Dark trays brown food faster than light ones.
Most recipes ask you to line the tray with baking paper or a silicone baking mat or grease it so food does not stick, and to space items apart so they bake evenly and do not spread into each other. You will see baking trays called for in baking and roasting recipes of all kinds.