Ajna (IAST: Ājñā) or third-eye chakra is the sixth primary chakra according to Hindu tradition.
The Ajna chakra is positioned in the stomata, directly behind the center of the forehead. Its ksehtram, or superficial activation site, is in the eyebrow region at the position of the "third eye."
Ajna is white in color, with two white petals. Inside the pericarp is the Shakti Hakini. It is depicted with a white moon, six faces, and six arms holding a book, a skull, a drum, and a rosary, while making the gestures associated with granting boons and dispelling fears. The downward pointing triangle above her contains a moon-white lingum. In some systems the deity Ardhanarishvara, a hermaphrodite form of Shiva-Shakti, symbolising the primordial duality of subject and object, resides within the lingum. Above that triangle is another smaller triangle containing the bija mantra, Aum.
Ajna translates as "command", and is considered the eye of intuition and intellect. When something is seen in the mind's eye, or in a dream, it is being seen by Ajna. It is a bridge that links gurus with disciples, allowing mind communication to occur between two people. The sense organ and action organ associated with Ajna is the mind.
As Hindus believe that spiritual energy from the environment enters their body through this gateway, they take great care to protect it with spiritually positive protecting forces. The various religious marks on the foreheads of men and women belonging to the Hindu faith (like holy ash, namam, vermilion etc.) are the blessed spiritual prasadam of their respective forms of the Hindu gods.
Meditation upon Ajna supposedly grants siddhis, or occult powers, to quickly enter another body at will and to become omniscient. He realizes unity with Brahman; and he has the ability to create, preserve, and destroy the three worlds.
In kundalini yoga, the practices said to stimulate the Ajna chakra include: Trataka (steady gazing), Shambhavi Mudra (gazing at the space between the eyebrows), and some forms of Pranayama (breath exercises).
Example via www.ramdass.org: Chakras in the Body