An Ethernet Tester is a device used to check the functionality and performance of Ethernet networks. It helps identify issues such as cable faults, misconfigurations, and connectivity problems. By sending signals through the network cables, it can determine if the connections are working properly and if the data is being transmitted effectively. These testers come in various types, ranging from simple handheld devices to more advanced models with additional features. Some can measure network speed, while others can test for specific protocols. Overall, an Ethernet Tester is essential for network technicians to ensure reliable and efficient network performance.