Theosis definition

Theosis ("deification," "divinization") is the process of a worshiper becoming free of hamartía ("missing the mark"), being united with God, beginning in this life and later consummated in bodily resurrection. For Orthodox Christians, Théōsis (see 2 Pet. 1:4) is salvation. Théōsis assumes that humans from the beginning are made to share in the Life or Nature of the all-Holy Trinity. Therefore, an infant or an adult worshiper is saved from the state of unholiness (hamartía — which is not to be confused with hamártēma “sin”) for participation in the Life (zōé, not simply bíos) of the Trinity — which is everlasting.

This is not to be confused with the heretical (apothéōsis) - "Deification in God’s Essence", which is imparticipable.