A fish finder is an electronic device used by anglers to locate fish underwater. It uses sonar technology to send sound waves into the water, which bounce off objects like fish and structures. The device then interprets these sound waves and displays the information on a screen, showing the depth and location of fish. Fish finders come in various models, from simple handheld units to advanced systems with GPS and mapping features. They are popular among recreational and professional fishermen, as they help improve fishing efficiency by identifying the best spots to catch fish, such as schools of fish or underwater structures.