A Ninja technique that only a member of the Uchiha clan can master. Sharingan is a sort of "evil eye" that can see through any ninjustsu technique, and also mentally damage an opponent through genjutsu (illusion techniques)

The Sharingan is a special type of dojutsu (pupil technique) that naturally occurs in all members of the Uchiha clan, though not all of them gain the ability to utilize it. The Sharingan is thought to be descended from the Byakugan, but grants the user different abilities and a different insight. The Sharingan's first and most well known ability is to memorize any technique that it is a witness to. It can memorize ninjutsu (ninja techniques), genjutsu (illusionary techniques), and taijutsu (hand-to-hand techniques) with perfect accuracy and allow the user to use the techniques, so long as they have the necessary resources to do so. Second, it has the ability to predict an opponent's movement, as well as allowing to track fast moving objects with great clarity. Third, it is capable of a unique brand of hypnosis that involves suggesting actions and thoughts to the opponent. Fourth, it can see through genjutsu, the level of which is possibly dependent on the user's skill.

In order to copy a jutsu, one has to have the physical ability to perform the technique. For example, they have to have the needed amount of chakra, stamina, agility, and/or strength in order to perform said technique. In addition to physical skill, the Sharingan cannot copy any other bloodline abilities or summon a creature the user has not made a contract with because the user of the Sharingan has to have the same blood as the other user.

The Sharingan does not automatically appear from birth in a us...

The Sharingan is a special ability found in the pupil of select members of the Uchiha clan. It is a pupil characteristic which is said to have been passed down from the Hyuuga's Byakugan, and then, with time, evolved.
The Sharingan has many abilities, but it's primary ability is to copy Nin, Gen, and Taijutsu.
There are two types of Sharingan. The underdeveloped Sharingan has two comma-like dots around the iris instead of the mastered Sharingan which has three. What is to be considered the Sharingan's ultimate ability is the Tsukiyomi.

1. A kekkei genkai, or bloodline limit, belonging to the Uchiha Clan (Kakashi Hatake is an exception. His sharingan was transplanted to him from Obito Uchiha, a former teammate. Because he does not have Uchiha blood, he cannot fully master the kekkei genkai).

2. To copy. Originating from the manga/anime Naruto.