Christianity is a religion. This religion is monotheistic, it means, there is only one (Greek: mono) God (Greek: theos).
There are three Abrahamic religions: Christianity, Judaism, and Islam.
Christians, the adherents of Christianity, believe that Jesus Christ is the Son of God and savior of all people, whose coming as the Messiah was prophesied in the Old Testament and chronicled in the New Testament.
Christianity is a trinitarian religion. The Trinity is the belief that God is one God in three persons, it means that the one God comprises three distinct, eternally co-existing persons: the Father (God the Father), the Son (God the Son, incarnate in Jesus Christ), and the Holy Spirit (God the Holy Spirit).