Ego

Ego is a Latin word meaning "I", cognate with the Greek Εγώ (Ego) meaning "I", often used in English to mean the "self", "identity" or other related concepts.

H. P. Blavatsky defined it as follows:

Ego (Lat.). “Self”; the consciousness in man “I am I”—or the feeling of “I-am-ship”. Esoteric philosophy teaches the existence of two Egos in man, the mortal or personal, and the Higher, the Divine and the Impersonal, calling the former “personality” and the latter “Individuality".

The quality of Ego-ship is a feature of the fifth principle, manas, and according to the plane in which it expresses it is qualified as "lower ego" (when in association with kama), as the "higher ego" (when on its own manasic plane), and as the "spiritual ego" when associated to buddhi.