[Sanskrit Avatāra “descent”, from avatarati “he descends”, from ava- “away” + tarati “he crosses over”] The incarnation of the Word; the descent or crossing-over of the Universal Christ from the plane of Spirit to the plane of Matter.
The Encyclopedia of Eastern Philosophy and Religion defines avatar as
an incarnation of divine consciousness on earth. An avatara is born not as the result of karma (as are ordinary human beings) but from an act of free will, and such a one is conscious of his divine mission throughout his life. He appears [in time of trouble] in order to establish new pathways for religious realization and to adapt them to the age in which he is born.
The avatar of an age
The avatar of an age is the Christ, the incarnation of the Son of God (Vishnu), the Second Person of the Trinity. The avatar, with his divine complement, Shakti, or twin flame, “outpictures” and “outplays” in consciousness and in the four lower bodies the archetypal pattern of the Father-Mother God for the evolution of souls in a two-thousand-year cycle.
The principal avatars of an age are two in number—the masculine and feminine prototypes who embody and show by their example the path of initiation designated by the solar hierarchies responsible for the lifewaves moving toward the center of the Cosmic Christ through the Open Door (the Teacher and Teaching) of that two-thousand-year dispensation. According to mankind’s karma, the evolutionary status quo of the children of God (their soul progress or lack of it in previous dispensations), and the requirements of the Logos, the Manus may designate numerous Christed ones—those endued with an extraordinary light—to go forth as world teachers and wayshowers.
The Christed ones demonstrate in a given epoch the Law of the Logos, stepped down through the Manu(s) and the avatar(s) until it is made flesh through their own Word and Work—to be ultimately victorious in its fulfillment in all souls of light sent forth to conquer time and space in that era.
Mark L. Prophet and Elizabeth Clare Prophet, Saint Germain On Alchemy: Formulas for Self-Transformation.
Pearls of Wisdom, vol. 38, no. 6, February 5, 1995, endnote.