What is the Third Eye and everything related to it? Is it real, and what is its ruling (Hukm)?

There is no such thing as a "third eye"; it is a pagan claim not mentioned in the Qur'an or Sunnah. What exists are insight (basirah), perspicacity (firasah), and inspiration (ilham), which are capabilities Allah bestows upon some of His servants. Insight is a power of the heart through which it perceives the realities of things. Perspicacity is a light Allah casts into the heart, enabling it to distinguish between truth and falsehood. Inspiration is a divine gift. One must be wary of attaching oneself to chakras, auras, and energy, as these are forms of paganism.