With an estimated 2.1 billion adherents, Christianity is the world's largest religion. Its origins are intertwined with Judaism, with which it shares much sacred text and early history; specifically, it shares the Hebrew Bible, known in the Christian context as the Old Testament. Christianity is considered an Abrahamic religion, along with Judaism.
In the Christian scriptures, the name "Christian" and so "Christianity" is first attested in Acts 11:26: "For a whole year they met with the church and taught a great many people.
And in Antioch Jesus' disciples were first called Christians" (Gr. χριστιανους, from Christ Gr. Χριστός, which means "the anointed").