The Vedic scriptures describe our antah karan (mind or ethereal heart) as having four aspects:
1) Mind (mana) It creates the thoughts, feelings, desires, hankerings, and aversions.
2) Intellect (buddhi) Its function is to analyse and decide. It understands, decides, and discriminates i.e. this is good, this is bad.
3) Subconscious mind (chitta) It is the storehouse of impressions and memories. It enables one to get attached to an object or person.
4) Ego (ahankar): It is the ego or ‘I’ness. It produces the sense of identity with the attributes of the body and creates pride.
These are not four separate entities, rather, they are simply four levels of functioning of the one mind. Hence, we may either refer to all of them together as the mind, or as the mind intellect, or as the mind-intellect-ego, or as the mind-intellect subconscious-ego mechanism. They all refer to the same thing.
Extracted from The Science of Mind Management by Swami Mukundananda