The word "trinity" comes from the word "tri" meaning three. For instance, tricycle means a cycle with three wheels. So the word "Trinity" simply means triune plus deity. It's a combination: tri-inity.
In Christianity, it is one word to describe the three entities that make up God. In Genesis, God says, "Let us make man in our image." This God is singular, but He's speaking of Himself in plural. There is God, the one God, of Abraham, Isaac, and Jacob.
And you have Jesus, or God's Son. When Jesus was baptized, God the Father says from heaven, "This is my beloved Son." Of course, God the Son is in the water. And then God the Spirit is descending. Jesus also taught the church to baptize in the name of God the Father, the Son, and the Spirit.
The teaching of one God made up of three persons is very biblical. Unfortunately, English speakers take the number one as a solely numerical idea. Yet in Hebrew, it could also mean simply unity. For instance, when a man and woman get married, they become "one flesh," but they are quite still two different people. But their union is one. This is what Jesus meant when He said, "Father I pray they might be one as we are one."
So don't let the word "one" confuse youthis is not polytheism as many charge. Christians worship one God. As Moses said, "Hear, oh Israel: the Lord our God is one." But Moses is also the one who wrote, "God said: 'Let us go down and confound their languages.' "
God the Father, Jesus the Son, and the Holy Spirit are one, united in their purpose of saving man. But they're obviously three different entities. Jesus while on earth prays to His Father in heaven. Jesus was neither a ventriloquist nor a schizophrenicHe was talking to His Father, and His Father answered Him. In the gospel of John, the disciples say, "We heard the Father answer Him."