Quinone is generally defined as an aromatic beneze molecule containing a double ketone functional group. Quinone is a common constituent of biologically relevant molecules (e.g. Vitamin K1 is phylloquinone) and serve as electron acceptors in electron transport chains such as those in Photosystem I & II, and aerobic respiration.

Benzoquinone refers to either of two cyclic isomers with the chemical formula C₆H₄O₂: orthobenzoquinone and parabenzoquinone.

orthobenzoquinone

parabenzoquinone

The word quinone can also be used for a family of molecules having a cycle with two double bonds similar to benzoquinone.