This is the spinning copy eye!

To understand the word "Sharingan", you have to read or watch the manga (comic book or cartoon series) Naruto. 
The story takes place in a retro-futuristic world imagined by its Japanese author Masashi Kishimoto. There are thirty-eight countries, and in twenty-two, there is a village that represents the military force, where families of ninjas and samurais live and train. There are nine creatures called "Tailed Demons", one of them, Kyubi, the nine-tailed demon, who took possession of half of the spirit of the newborn Naruto, during the attack of his village in the land of fire, Konoha, where the Uchiwa clan lives. 
Naruto will then train to become Hokage (leader of his village) with his friends Sakura and Sasuke and their teacher Kakashi. 

The Sharingan

This Japanese word means "spinning copy eye". It is one of the ninja fighting techniques using the eyes, called dôjutsu : Byakugan (white eye), Jôgan (pupil not very visible), Ketsuryûgan (reddish), Mangekyo Sharingan (spinning copy eye), Kekkei Genkai of Ranmaru (red iris), Rinne Sharingan (ancestor of Sharingan), Senrigan (clairvoyance), Tenseigan (Eye of reincarnation), Shion (purple, divination), Yome (dilated pupil) and the Sharingan, the spinning copy eye of red color. 
Complicated isn't it!

This eye mutation is hereditary in the Uchiwa clan. It is, with the Byakugan and the Rinnegan, one of the three great dôjutsu. Also called "celestial pupil" or "eye that reflects the heart or feelings", it is acquired when one knows love and when one loses it, it transforms into hatred and gives rise to a special chakra that affects the optical nerves. The Sharingan can be grafted to a person who is not Uchiwa but he will need more chakra to activate it.

Ability of the Sharingan

• The insight that allows to see through and detect the weaknesses of the enemy, to read lips, to anticipate the movements of the opponent.
• Hypnotism which allows to take control of the opponent's body. 
• To distort reality to escape death by modifying destiny
• Trapping in an infinite loop

If you want to talk about this and learn how to draw it, come to Apolline manga drawing lesson!