Short answers, pulled from the story.
Baptism is a Christian rite of initiation performed with water, regarded as a sacrament in most churches and an ordinance in others. It is important because most Christian traditions hold it necessary for salvation or as the formal entry into church membership, and because it unites Christians across denominations through the shared Trinitarian formula.
Baptism emerged from Jewish ritualistic washing practices during the Second Temple period. Texts in the Dead Sea Scrolls, such as the Rule of the Community, describe ritual cleansing with water for purification. John the Baptist took these practices and made water baptism the central sacrament of his messianic movement, from which Christian baptism developed.
The three main modes are aspersion (sprinkling water on the head), affusion (pouring water over the head), and immersion or submersion (placing the candidate partially or fully under water). The Didache, dated between AD 60 and 150, already acknowledged all three as acceptable. Affusion became standard in Western Europe between the twelfth and fourteenth centuries, while submersion remains the norm in Orthodox and Baptist traditions.
The English word baptism derives through Latin from the Greek báptisma, a neologism coined in the New Testament. It comes from the verb baptízō, which in Hellenistic usage meant immersion, going under, or perishing - as in a ship sinking or a person drowning. The Greek-English Lexicon of Liddell and Scott gives "dip, plunge" as the primary meaning of baptízein.
Quakers, some Unitarians (in particular Unitarian Universalists), and The Salvation Army do not practice water baptism at all. Outside Christianity, Mandaeans undergo repeated water baptism for purification rather than initiation, and consider John the Baptist their greatest prophet.
No. The Catholic, Orthodox, Lutheran, Anglican, Presbyterian, and Methodist churches generally recognize baptisms performed with water and the Trinitarian formula across their traditions. However, they all declare the baptism of the Church of Jesus Christ of Latter-day Saints invalid due to differing concepts of the Trinity. Oneness Pentecostals, who baptize only in Jesus' name rather than the Trinitarian formula, are also excluded from mutual recognition.