Unsaturated refers to a hydrocarbon with at least one double or triple bond. An alkene is a hydrocarbon with at least one double bond and the general formula CnH2n. An alkyne is a hydrocarbon with at least one triple bond and the general formula CnH2n+2.
Ethene, benzene and acetic acid are examples of unsaturated hydrocarbons. Alkenes and alkynes are non polar compounds and have low boiling points and low melting points, with alkynes having slightly higher boiling points than alkenes. The double bond in an alkene makes it have fewer hydrogen atoms than a compound that is saturated, which is one containing only single carbon-carbon bonds.