1. n. [Heavy Oil]
A sand body that contains heavy hydrocarbon residues such as tar or asphalt, or degraded oil that has lost its volatile components. Hydrocarbons can be liberated from tar sands by heating and other processes, but tar sands, such as the Athabasca tar sands of Canada, are not commonly commercial because of high costs of production. Among some workers in the field of heavy oil, this term is falling out of use, in favor of the term "oil sand."
See: asphalt, bitumen, hydrocarbon, oil sand