From Latin sub- "under, below, beneath" + conscious "knowing, aware" to indicate the psychological part of ourselves that we are unaware of. In Vedanta, "chitta."
"Subconsciousness resulted from our wrong ways and means of living. Our subconsciousness should be consciousness, but unfortunately we live so mistakenly that one of our two parts sleep deeply and is called subconsciousness. The subconsciousness works especially during the sleep of the physical body; if that subconsciousness would awaken and all of it become consciousness, then it is clear that during the hours of sleep we would live fully awakened in the higher dimensions of space. Besides the physical body, the human being possesses a molecular body with which he travels during the hours of sleep to a very far distances; unfortunately our subconsciousness only allows us to have subconscious, subjective experiences, which are known as dreams. Whosoever wants to become cognizant during their dreaming state must become cognizant of his second half, called subconsciousness. If the subconsciousness becomes consciousness, we have then access to the transcendental knowledge of the higher dimensions of space." - Samael Aun Weor, Consciousness