Unsaturated compounds consist of molecules with carbon atoms being linked by doule (or tripple) bonds.
Unsaturated means that molecules of these compounds are "hungry" to join with atoms of other molecules:

* Ethine molecules react with bromine-molecules from bromine water.
* Ethene molecules can react with many other ethene molecules to form a
   polyethylene molecule.
* Oleic acid is an unsaturated fatty acid.