from http://userpages.aug.com/~mdkersey/Theosis.html
An easy definition for Theosis is: "Union with God". St Paul tells us in 2 Corinthians 3:18 "But we all, with open face beholding as in a glass the glory of the Lord, are changed into the same image from glory to glory, even as by the Spirit of the Lord"....Rev. Dr. Stanley Harakas relates to Theosis and becoming a saint with "a term in Orthodox Christian teaching which describes that believer who has deeply bonded his life with God, who worships and communes with God, and who feels, wills and acts in harmony with Gods life and will" ...
What would you add or take away from that?
Not much. One thing comes to mind" dying unto the world and especially oneself. It is a process, a life-long journey of purification, characterized by humility, and selflessness, ever more in harmony with God's will, ever-more Christ-like.
In fact, Orthodoxy defines being "saved" not by proclaiming Christ our Lord and Savior, but how Christ-like we have become following Him at the end of our journey.