The line-crossing ceremony is an initiation rite that commemorates a person's first crossing of the Equator. The tradition may have originated with ceremonies when passing headlands, and become a "folly" sanctioned as a boost to morale, or have been created as a test for seasoned sailors to ensure their new shipmates were capable of handling long, rough voyages. Equator-crossing ceremonies, typically featuring King Neptune, are common in the Navy and are also sometimes carried out for passengers' entertainment on civilian ocean liners and cruise ships. They are also performed in the merchant navy and aboard sail training ships.

Initiation is a rite of passage marking entrance or acceptance into a group or society. It could also be a formal admission to adulthood in a community or one of its formal components. In an extended sense, it can also signify a transformation in which the initiate is 'reborn' into a new role. Examples of initiation ceremonies might include Christian baptism or confirmation, Jewish bar or bat mitzvah, acceptance into a fraternal organization, secret society or religious order, or graduation from school or recruit training. A person taking the initiation ceremony in traditional rites, such as those depicted in these pictures, is called an initiate.