The Egyptians conceived of humans as composed of nine parts: the physical body and eight divisions of non-physical attributes, what we may call the soul.
Khat is the physical body. It is only the material substance of the body, with no volition, consciousness or will. (Aufu is also the physical body, but it is only associated with a living body, while khat refers to the body whether it is alive or not.)
The ka is the double. It is closely associated with the physical body, and it embodies the instincts and imagination. Human experience is a product of interaction between the person and the environment. The ka is the mediating force between the body and environment that interprets experience. This is not the etheric double of theosophy. The imagination of the ka is not creative. It does not correspond with creative visualization.
The ab is the heart, the seat of the emotions and passions. It is the seat of the ba.
The ba is the spirit of the person. It is closely associated with the heart and is sometimes called the heart-soul. It is the source of the will.
The khaibit (or haidit) is the shadow. This is the vehicle for the ba, the seat of the unconscious and the source of most human creativity, dreams and hallucinations.
The sekhem is the vitality or life force of the body, the electrical impulses in the nerves that animate the body. It is also the vitality of the immortal spirit, or khu.
The sahu is the spiritual body, the vehicle for the khu.
The khu, also called the Shining One, is the soul of the spiritual body.
The ren is the Name, or the true name of the person. This is not the name other people know you by. It is, for lack of a better word, your spirit name. It is more of an essence than a word, a kind of energy signature. Tradition said that if you knew the Name (ren) of someone--even a god--you had their powers (neter or netjer) and could control them. This is where the concept of words of power comes from, and it is the origin of the tradition within Judaism for the taboo against speaking the true name of God, and within pagan traditions for the secrecy surrounding one's full magickal name. The ren is the seat of the khu.