Automatic Repeat reQuest (ARQ) is a communication protocol used in data transmission to ensure reliable delivery of messages. When a sender transmits data, the receiver checks for errors. If an error is detected, the receiver requests the sender to resend the corrupted data. This process helps maintain the integrity of the information being communicated. ARQ is commonly used in various networking protocols, including TCP (Transmission Control Protocol) and Wi-Fi. By implementing ARQ, systems can effectively manage data loss and ensure that all transmitted information is received correctly, enhancing overall communication reliability.