The Trinity is God as revealed in the Bible.
The Bible doesn't give us a systematic statement of the doctrine of the Trinity. But that doesn't mean the Trinity is not biblical.
In The Biblical Trinity: Encountering the Father, Son, and Holy Spirit in Scripture, Brandon D. Smith proclaims the Trinity from the Bible. The doctrine arises not from a handful of prooftexts but from the fullness of what the Bible says about God.
Through short reflections on fifteen key New Testament passages in conversation with the Old Testament, Smith shows how God's word reveals the Trinity. The book concludes with three rules for how to encounter the truth and beauty of our Triune God in all of Scripture.