The word "Trinity" does not appear anywhere in scriptures, however, the bible does refer to the Father, Son, and Holy Spirit in John 14:26 – 15:26, 2Corinthians 13:14, and 1 Peter 1:2. We use the word Trinity to describe the Father, Son and Holy Spirit.
From a Christian worldview, the Father is God Almighty. Jesus Christ is God Almighty in the flesh. And the Holy Spirit is the Spirit of God Almighty who comes to live in us when we accept Jesus as Lord and Savior.
While some are skeptical about the three being one, I would like to illustrate that H20 is the chemical formula for water. As such, it too has three entities. Consider that when water is in its 1st state, it is a fluid. In its 2nd state, "frozen water" is solid as a rock. In its 3rd state, when heat is applied to it, water is a steaming vapor.
So you can see by this illustration the Trinity is three in one, and is possible even from a secular worldview as illustrated with water.