If you mention the word ‘TRINITY’ to a group of theologians, or to some Scripture scholars, they will probably give you some lengthy explanations.
Exegetes, theology professors, spiritual authors will probably do the same.
Definitions and explanations, are their domain.
Expounding on concepts and themes is very much part of their expertise. 
Strangely enough, if you look for the word ‘TRINITY’ in the Bible, you will NOT find it!
You may think that it is amazing but it is true.
This word came to be used in the Christian language only late in the fourth century.
It was at that time that this term was used to express the faith of Christian believers.
But, you will find, yes, you will discover in the New Testament, the expression of this REALITY of a God who is one and who manifests Itself (this pronoun is not masculine or feminine) in three Persons.
It is in the chapters 14 to 17 of the gospel of John that we can perceive this most clearly.
There, we hear Jesus repeatedly speaking of the FATHER and of the SPIRIT as being one and himself being one with them.
The first reading of this feast of the Holy Trinity (Ex.34:4-6,8-9) tells us that God is “a God of tenderness and compassion, rich in kindness and faithfulness.”
So, what we celebrate on Trinity Sunday is this tenderness and compassion reaching us in a fatherly way, in the brotherly way of a Saviour, in the way of One who is our Advocate – for this is what they are to us and for us: the Father, the Son and the Spirit.
What more could be said?