What is Medusa in greek mythology?

in Greek mythology Medusa was one of the three Gorgon's, the youngest and the only one who was mortal, she could turn people to stone just by looking at them. before her statue making days she was the girlfriend of the god of the sea Poseidon. they offended the goddess Athena by meeting up in her temple, not being powerful enough to take revenge on Poseidon she turned Medusa and her 2 sisters who helped her get into the temple into the three Gorgon's.