Although the words christening and baptism are often used interchangeably, baptism refers to a holy Christian sacrament in which water is used to claim the child in Jesus' name, and a christening refers to a ceremony in which the infant is officially given a name. Just as with baptisms, many christenings incorporate holy water, leading some to suggest that all christenings are baptisms, although this is not the case.
The baptism ceremony preceded Christianity, as baptism rituals were performed by the ancient Greeks for purification for at least 100 years before the birth of Christ. These early baptisms were usually performed on adults, and it wasn't until the third century A.D. that the baptizing of infants became a standard Christian practice.
Although baptism has been around for more than 2,000 years, christening ceremonies are much more recent and began sometime around the 14th century. Christening has religious roots, hence the use of the word "Christ" in the ceremony's name. Baptism ceremonies were usually a way to incorporate both the baptism and naming of the child into one. It is not only people that can be christened, as these ceremonies are also held for the naming of ships, houses and other personal property.