Asphalt, or bitumen, is a sticky, black and highly viscous liquid or semi-solid, composed almost entirely of petroleum. It is present in most crude petroleums and in some natural deposits. It is the material which made the La Brea tar pits.
Its main use is in road construction. Mixed with "aggregate" (sand, gravel, crushed stone, etc.) it makes a good road surface. It has various other names: pitch, tarmac, blacktop, asphalt concrete, asphalt pavement (US), all mean roughly the same thing.