The word "testament" (from the Latin testamentum, translating the Greek diatheke and Hebrew berith) means a covenant, pact, or solemn agreement. It is used to designate the two main divisions of Sacred Scripture: the Old Testament and the New Testament (CCC 120).
Old and New
The Old Testament records the covenants God made with Israel, laying the foundation and preparing the way for the Messiah. The New Testament records the definitive and eternal covenant established in the blood of Jesus Christ. The Church teaches that the two Testaments form an unbreakable unity, and the Old is revealed fully only in the light of the New (CCC 121, 128-129).
May the Lord bless you and keep you.