In the Marvel Cinematic Universe (MCU), the third eye in Doctor Strange refers to the Eye of Agamotto, a powerful magical artifact that is entrusted to the Sorcerer Supreme. The Eye of Agamotto is a golden amulet that contains a green gemstone, which is said to contain the power of the Time Stone.
In the MCU, the third eye is first introduced in the 2016 film Doctor Strange, which follows the journey of neurosurgeon Dr. Stephen Strange (played by Benedict Cumberbatch) as he discovers the world of magic and becomes the Sorcerer Supreme. In the film, the Eye of Agamotto is given to Strange by his mentor, the Ancient One (played by Tilda Swinton), who explains that it can be used to manipulate time and alter the course of events.
Throughout the film, Strange uses the Eye of Agamotto to battle the villainous Kaecilius (played by Mads Mikkelsen), who seeks to harness the power of the Dark Dimension and bring about the destruction of the universe. In one pivotal scene, Strange uses the Eye to reverse time and prevent the destruction of Hong Kong, using the power of the Time Stone to manipulate events and create a new timeline.
In addition to its role in the film, the Eye of Agamotto has played a significant role in the wider MCU. It is prominently featured in the 2018 film Avengers: Infinity War, where it is used by Strange to view possible futures and ultimately to defeat the villainous Thanos (played by Josh Brolin). In this film, the Eye is revealed to be one of the six Infinity Stones, which are powerful artifacts that each contain a different aspect of the universe: Space, Reality, Power, Mind, Time, and Soul.
Overall, the third eye in Doctor Strange refers to the Eye of Agamotto, a powerful magical artifact that is entrusted to the Sorcerer Supreme. It is used by Doctor Strange and other characters in the MCU to manipulate time, view possible futures, and battle powerful villains. As one of the six Infinity Stones, the Eye of Agamotto plays a significant role in the wider MCU and its ongoing narrative.