a Christian ceremony in which a few drops of water are poured on somebody or they are covered with water, to welcome them into the Christian Church and often to name them （基督教的）洗礼，浸礼 Word OriginMiddle English: from Old French baptesme, via ecclesiastical Latin from ecclesiastical Greek baptismos ‘ceremonial washing’, from baptizein ‘immerse, baptize’.
Idioms
a baptism of fire
a difficult introduction to a new job or activity 重大的考验；战火的洗礼