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 user; instead, it will usually appear when the user is in a life threatening situation, where the power of the Sharingan could save the user. After this first appearance, the user can then call up the Sharingan any time he or she pleases. (Due to its unique nature, Kakashi's Sharingan is "permanently on", and thus he covers it except during heated battles, to conserve chakra.) The power of the Sharingan is judged through the number of tomoe in the person's eye. It is not unheard of for a Sharingan user to have different amounts of tomoe in each eye. For example, Sasuke's Sharingan initially had two tomoe in one eye and one in the other. Eventually his Sharingan evolved to two tomoe in each eye, then three. A fully-matured Sharingan has three tomoe in each eye.

Interestingly enough, it is possible to transplant Sharingan eyes from one person to another, as occurred with Kakashi and his deceased comrade Obito. However, transplanted eyes do not work as well in a non-Uchiha body, causing much more strain on the user, as is the case with Kakashi - extended use of his Sharingan will cause him to collapse. Uchiha clan members are not burdened with this weakness; while activation of the Sharingan does consume chakra, the drain is so small as to be almost insignificant. Uchiha Itachi in particular seems to have no trouble in keeping his Sharingan activated near-constantly.

Characters who currently possess the Sharingan include Uchiha Sasuke, Uchiha Itachi, and Hatake Kakashi. Kakashi's eye was given to him by Uchiha Obito, one of his teammates in his original three-man ninja team. Obito developed it in battle against rival Rock shinobi and during this battle Kakashi lost his left eye when he was attacked, which is also the reason for his scar there. Near the end of the battle Obito's right side is crushed under a giant rock, and as his last act Obito has Rin, a medical ninja, remove his left eye and implant it in Kakashi's left eye, thus allowing Kakashi to use the Sharingan even though he does not have Uchiha blood. This is also why only his left eye is a Sharingan eye.

Hax.

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.

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.

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 an abilllity from the animie sieries "Naruto" and it comes from the blood line of the "Uchiha Clan" its a eye that lets a ninja know EVERYTHING THERE OPONET IS GOING TO DO so they can doge it or copy everything there oponet does faster then there enemy thinks it through so technekly you know the future of your enemy for example lets say naruto is going to do a shadow clone justu then sasuske uchiha get his sharingan and knows what naruto is going to do then he does more shadow clones and does it before naruto even thinks about doing it ill put a giphy of the shringan eye

when the sides of your eyes or whole eyes are yellow because of liver failure.

Mangekyou Sharingan is translated as Kaleidoscope Copy Wheel Eye. It is a higher form of the Uchiha clan's sharingan. The basic sharingan will enable the user to memorize any technique that it has been a witness to including ninjutsu, genjutsu, and taijutsu techniques it can also enable the user to see through and illusionary technique. With the Mangekyou Sharingan activated, one major advantage is to be able to use the three most powerful jutsu possible, tsukuyomi, amaterasu, and susanoo. The disadvantage of the Mangekyou Sharingan is, it causes the deterioration of the eyes.

When someone is so good at guitar they immidiately listen to a song and play it without any written music. Comes from popular anime series naruto in which ninja who possess sharingan can immidiately mimmick their opponents attacks without even seeing them.