A cable tester is a device used to check the integrity and functionality of various types of cables, such as Ethernet or coaxial cables. It helps identify issues like shorts, opens, or miswiring, ensuring that the cables are properly connected and functioning as intended. These testers typically consist of a main unit and a remote unit, which work together to send signals through the cable. By analyzing the signals received, the tester can provide information about the cable's condition, making it an essential tool for network technicians and telecommunications professionals.