(Sanskrit अन्तःकरण, literally "inner organ, instrument, conscience, mind, heart, soul, seat of thought and feeling") In Hinduism, our psychological-spiritual structure, comprised of manas, buddhi, chitta, and ahamkara.
"Antahkarana is a term used by the Vedantins to include mind, Buddhi, Chitta and Ahankara. When used in a broad sense, it means the internal instrument. 'Antah' means internal; 'Karana' means instrument. It is the inner instrument (as distinguished from the term Bahya Karana, outer instrument or the senses or Indriyas) through which you sense, perceive, think and reason out." - Swami Sivananda
Antahkarana is the name of the "silver cord" that joins the physical body with the internal bodies.
"...or ever the silver cord be loosed, or the golden bowl be broken, or the pitcher be broken at the fountain, or the wheel broken at the cistern. Then shall the dust return to the earth as it was: and the spirit shall return unto God who gave it." —Ecclesiastes 12
"When the bridge called "Antahkarana," which communicates the divine triad with its "inferior essence," is broken, the inferior essence (trapped into the ego) is left separated and is sunk into the abyss of destructive forces, where it (its ego) disintegrates little by little." - Samael Aun Weor, The Zodiacal Course