Why is ethylene called unsaturated hydro carbon

In small quantities, ethylene is used as an anesthetic agent which is used to hasten the ripping of fruit. Ethylene has a double bond between the carbons so it is classified as unsaturated hydrocarbon.

i) Why is ethene called an unsaturated hydrocarbon?

Ethylene (or IUPAC name ethene) is the simplest alkene hydrocarbon, consisting of four hydrogen atoms and two carbon atoms connected by a double bond. Because it contains a double bond, ethylene is called an unsaturated hydrocarbon or an olefin.

ii) Why are hydrocarbons unsaturated?

Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bonds between adjacent carbon atoms. The term "unsaturated" means more hydrogen atoms may be added to the hydrocarbon to make it saturated (i.e. consisting all single bonds).