As defined in RFC 768, a UDP is a connectionless protocol, which is great for transmitting real-time data between hosts and is often termed as an unreliable form of communication. The reason is, UDP doesn't care about the delivery of packets, and any lost packets are not recovered because the sender is never informed about the dropped or discarded packets. However, many protocols such as DNS, TFTP, SIP, and so on. rely only on this.
The protocols that use UDP as a transport mechanism should rely upon other techniques to ensure data delivery and error-checking. A point to note is that UDP provides faster transmission of packets as it does not perform three-way handshake or graceful termination as observed in the TCP. UDP is referred to as a transaction-oriented protocol and not a message-oriented protocike a Tol lCP.