The definition of the Trinity is that there is only one God, but in the unity of the Godhead there are three eternal and coequal Persons, the same in substance but distinct in subsistence.

The Old Testament reveals the Trinity. This includes passages which use the plural word Elohim and plural pronouns referring to God (Genesis 1:1, 26; Isaiah 6:8).In the New Testament there is clear revelation that the Father, Son, and Spirit are God, thus a Triunity or Trinity (neither is a Biblical word).  The Father is God (John 6:27; Ephesians 4:6).  Jesus Christ is God (Hebrews 1:8).  The Spirit is God (Acts 5:3-4).  The three Persons are equal and one (Matthew 28:19; II Corinthians 13:14).  “For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one” (I John 5:7).