Three in One

Its called perichoresis, its a word that describes the three in one nature of God. The term was originated by Saint Gregory Nazianzus who was a contemporary of Saint John Chrysostom. Saint Gregory was a second generation bishop, because in those days both priests and bishops could be married. Like Saint John he defended the Church against the Arian heresy. He was a teacher of Saint Jerome.
The Latinized version is Circuminsession. It means that the Father and the Son and the Holy Spirit have reciprocal inexistence and compenetration of their Three Persons. They are, as we say in the creed, of one substance with the Father.