A relay card is a crucial electronic component used in automation and control systems to manage multiple electrical circuits. It consists of multiple relays mounted on a single card, which can be controlled remotely via a microcontroller, PLC, or other automation systems. Relay cards are designed to switch electrical loads on and off without direct manual intervention, making them ideal for applications that require automated control, such as in industrial machinery, security systems, and home automation. By providing electrical isolation between control circuits and high-power loads, relay cards help protect sensitive electronics and ensure safe operation in various environments.