A lighthouse is a tower or similar structure built with the primary purpose of holding a navigation light. Most lighthouses are located along the coastlines of oceans and major lakes where ship travel occurs. The light may be used to guide ships along known routes, or to warn ships against approaching shores or shallow waters.

The navigation light is the primary reason for the structure. Its role can be route guidance or warning of a nearby shoreline or shallow water.

Ocean and lake shorelines are common settings. A light placed on a structure designed primarily for another purpose does not alone establish the lighthouse form.