A sacrament is a sacred rite recognized as of particular importance and significance. There are various views on the existence and meaning of such rites.
Baptism (from the Greek noun βάπτισμα baptisma; itself derived from βαπτισμός baptismos, washing) is a Christian rite of admission (or adoption), almost invariably with the use of water, into the Christian Church generally and also a particular church tradition. Baptism has been called a sacrament and an ordinance of Jesus Christ. In some traditions, baptism is also called christening, but for others the word "christening" is reserved for the baptism of infants.
The New Testament reports that Jesus was baptized. The usual form of baptism among the earliest Christians was for the naked candidate to be immersed totally (submersion) or partially (standing or kneeling in water while water was poured on him or her). While John the Baptist's use of a deep river for his baptism suggests immersion, pictorial and archaeological evidence of Christian baptism from the 3rd century onward indicates that a normal form was to have the candidate stand in water while water was poured over the upper body. Other common forms of baptism now in use include pouring water three times on the forehead.
Martyrdom was identified early in Church history as "baptism by blood", enabling martyrs who had not been baptized by water to be saved. Later, the Catholic Church identified a baptism of desire, by which those preparing for baptism who die before actually receiving the sacrament are considered saved. As evidenced also in the common Christian practice of infant baptism, baptism was universally seen by Christians as in some sense necessary for salvation, until Huldrych Zwingli in the 16th century denied its necessity.