Christendom, or the Christian world, has several meanings. In a cultural sense it refers to the worldwide community of Christians, adherents of Christianity. In a historical or geopolitical sense the term usually refers collectively to Christian majority countries or countries in which Christianity dominates or was a territorial phenomenon.

The term Christendom is developed from the Latin word Christianus. The Christian world is also known collectively as the Corpus Christianum. The Latin term Corpus Christianum is often translated as the Christian body, meaning the community of all Christians. The Christian polity, embodying a less secular meaning, can be compatible with the idea of both a religious and a temporal body: Corpus Christianum. The Corpus Christianum can be seen as a Christian equivalent of the Muslim Ummah. The Kingdom of God is also frequently used, denoting that the Christian world is within (or among) people.