As a noun, Christian is an appellation deriving from the name "Christ" and is derived from the Greek noun Christos which means "anointed one," itself a translation of the Hebrew word Moshiach or "Messiah."

"Christian" also means a member or adherent of a church or other organized group within Christianity. As an adjective, the term may also describe anything associated with Christianity, or even remotely thought to be consistent with Christianity, as in "the Christian thing to do."

Who is a Christian?

The definition of who is a "Christian" varies among different Christian groups. Roman Catholics, Eastern Orthodox, and many Protestants define a Christian as one who has become a member of the Church through the sacrament of baptism. In these churches, infants who are baptized may be considered Christians, although they are expected to make a personal affirmation of faith when old enough to decide for themselves.

Evangelical and fundamentalist denominations do not practice infant baptism and do not believe that baptism is connected with salvation (a sacrament). Rather, they consider it to be a public voluntary act of identifying oneself with Jesus Christ. They encourage youth and adults to "become Christians" by personally "accepting Jesus Christ as their Lord and Savior," and to follow that decision with Believer's Baptism. These groups also use the phrase "born-again" (John 3:3) to describe becoming a Christian.

A few denominations and sects teach that Believer's baptism is necessary for salvation — the transition from non-Christian to Christian (see Baptismal regeneration). They define a Christian as one who has been baptized as a repenting adult.

Within countries where Christianity is the historical majority religion, the term is also used by some in a casual generic sense to indicate that they are not members of nor affiliated with any other religion – therefore considering themselves Christians by default.

In other languages

As the identification of "Christ" with Jesus is not accepted within Judaism, in the Hebrew language Christians are called "Nazarenes" (Natsri), because Jesus is described in the New Testament as being from the province of Nazareth.

In Arabic and other languages influenced by Muslim culture, two words are commonly used for Christians: Nasrani, again referring to Nazareth, and Masihi meaning followers of the Messiah. Where there is a distinction, Nasrani refers to people from a Christian culture and Masihi means those with a religious faith in Jesus. In some countries Nasrani tends to be used generically for non-Muslim white people. Another Arabic word sometimes used for Christians, particularly in a political context, is Salibi; this refers to Crusaders and has negative connotations.