Rock sliders Wikipedia
Rock sliders are an aftermarket accessory popular among four wheel drive vehicle owners who engage in more serious off-road driving.
Rock sliders are typically made of heavy-duty box section steel, although they can also be made from tubular steel as well. They run along each side of the vehicle, from just behind the front wheel to just before the rear wheel, just below the level of the door sills. They are affixed to the vehicle's chassis, and their function is to protect the door sills and door bottoms from damage when crossing large obstacles (such as rocks - hence the name).