Baptism is a specifically Christian thing, but it originated as part of the ritual for conversion to Judaism. Converts to Judaism must immerse themselves in a mikvah, a ritual bath. This is quite similar to the ritual baths used by those Cristian denominations that practice adult baptism with full immersion. (Historically, Christians only began to do infant baptism by a sprinkle of water about 1000 years ago.) Those who are born Jewish may immerse themselves for other reasons -- The Bible has numerous commandments that ask for immersion as a purification ritual. Jewish boys undergo circumcision at age 8 days. That biblically mandated ritual marks the entry of a boy into the covenant of Abraham, and socially, it holds a place similar to infant baptism in Christianity.