Baptism is a religious ceremony in which a person is welcomed into the Christian faith, usually by being sprinkled with water or briefly immersed in it. The water symbolizes spiritual cleansing and a fresh start. In many Christian churches, babies are baptized as a way for their parents to dedicate them to God and promise to raise them in the faith. In other Christian traditions, people wait until they're old enough to choose baptism for themselves, often as teenagers or adults.

The ceremony itself can vary. Sometimes a minister sprinkles or pours water on the person's forehead. Other times, the person is fully dunked underwater in a baptismal pool or even a river, as Jesus was baptized in the Jordan River according to Christian scripture. Family and friends often gather to witness and celebrate the occasion.

Outside of religion, people use the phrase baptism by fire to describe learning something the hard way, through a difficult first experience. A new teacher facing a chaotic classroom on her first day might call it a baptism by fire. The phrase comes from the idea that sometimes you learn best by being thrown right into a challenging situation, though it has nothing to do with the religious ceremony itself.