The term 'road-paving stuff' refers to materials used in the process of paving roads. The most common material used is TAR, which is a viscous black liquid made from coal, wood, or petroleum. TAR is used to bind together the stones and gravel that make up the road surface, and it also helps to protect the road from water damage. TAR is also used to fill in cracks and crevices in the road surface, making it smoother and more durable.