Christianity has 4 different meanings across 2 categories:
a monotheistic system of beliefs and practices based on the Old Testament and the teachings of Jesus as embodied in the New Testament and emphasizing the role of Jesus as savior
"Christianity is a monotheistic religion that centers on the life and teachings of Jesus as the divine savior."
the collective body of Christians throughout the world and history (found predominantly in Europe and the Americas and Australia)
"for a thousand years the Roman Catholic Church was the principal church of Christendom"
An Abrahamic religion originating from the community of the followers of Jesus Christ.
"The medieval map depicted the political boundaries of Christendom, showing where Christian kingdoms held power against Islamic states."
Christendom
The word comes from the Ancient Greek Khristianós, which combined the name for Christ with a suffix meaning "of or related to." It eventually entered English via Old French and Medieval Latin, evolving into the modern term for followers of Christ.