1. n. 
The group of hydrocarbon compounds that has one or more double or triple bonds between carbon atoms in the linear chain. Ethylene, C2H4, is the smallest olefin. Synthetic olefinic hydrocarbons are made by polymerization of ethylene under catalytic conditions. They are used in synthetic-base mud and as lubricants for water muds.
See: aliphatic compound, aromatic hydrocarbon, emulsion mud, isomerized olefin, linear alphaolefin, naphthenic hydrocarbon, paraffinic hydrocarbon, polyalphaolefin, syn, synthetic-base fluid, synthetic-base mud