User Datagram Protocol (UDP) is a communication protocol used for sending data over a network. Unlike Transmission Control Protocol (TCP), UDP does not establish a connection before sending data, making it faster but less reliable. It sends data in small packets called datagrams, which can arrive out of order or not at all. UDP is commonly used in applications where speed is crucial, such as online gaming, video streaming, and voice over IP (VoIP). These applications can tolerate some data loss, so the benefits of reduced latency outweigh the risks of missing packets.