A sailor is also known as a mariner or a seaman. Sailors work on passenger ships, freighters, and tanker ships. A sailor navigates sea-going vessels and assists with the maintenance, operation, and service of these vessels. The term sailor was derived from the fact that all water-borne vessels were once powered by sails. Now the term encompasses all types of vessels, no matter how they are powered. Today, sailors may work for the military or private companies in all aspects of marine employment.