The brake drum is a metal drum that fits over the brake shoes and rotates at wheel speed. When the brakes are applied, the brake shoes are forced against the inside of the brake drum, which slows or stops the vehicle. Most modern vehicles only use brake drums on the rear wheels.
The most common problem with the brake drums are grooves worn into the brake drum from brake shoe material wearing off completely exposing the metal backing. If grooves are worn into the brake drum then it will either need to be resurfaced or replaced.
Since brake drums are considered wear and tear items, manufacturer factory warranties and extended auto warranties will not cover them. However, there are maintenance plans available that will inspect the brake shoes. By inspecting the brake shoes for wear, they can be replaced before wearing completely off and damaging the brake drum.