A compound containing only hydrogen and carbon, e.g. methane
Hydrocarbons are often alkanes or alkenes. Alkanes only have single bonds throughout their structure ("saturated hydrocarbons") whereas alkenes have double bonds (unstaurated hydrocarbons). You can tell if a hydrocarbon is an alkane or an alkene by their name - for example, ethane is an alkane whereas ethene is an alkene and therefore has a double bond.