The word oak can refer to:

• An oak tree, genus Quercus.
• The Australian tree known as she-oak or desert-oak is unrelated, and instead belongs to the genus Allocasuarina.
• The American plant known as poison-oak is also unrelated, belonging to the genus Toxicodendron.

• The town of Oak, Nebraska, USA.

• OAK is also the three-letter IATA airport code for Oakland International Airport in Oakland, California USA.