The New Testament’s 29 books, formally assembled in mid-2nd century, was at that time placed alongside the Hebrew Scriptures (Old Testament), creating a Christian Bible. About 200 A.D. a priest named Tertullian coined the phrase Novum Testamentum.
The O.T. was written primarily in Hebrew -- the N.T. in Greek, the language of the first century Graeco-Roman world.
Together, these two testaments comprise the book that’s unique among the sacred literature of all religions