Asphalt ( or , occasionally ), also known as bitumen (, ) is a sticky, black and highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product; it is a substance classed as a pitch. Until the 20th century, the term asphaltum was also used. The word is derived from the Ancient Greek ἄσφαλτος ásphaltos (itself perhaps an Eastern word, though see "Etymology" below).