Note: The following is an excerpt from the official IETF RFC. It is provided here as a convenience and is not authoritative. Refer to the original document as the authoritative reference.
Introduction
This User Datagram Protocol (UDP) is defined to make available a
datagram mode of packet-switched computer communication in the
environment of an interconnected set of computer networks. This
protocol assumes that the Internet Protocol (IP)1)
is used as the underlying protocol.
This protocol provides a procedure for application programs to send
messages to other programs with a minimum of protocol mechanism. The
protocol is transaction oriented, and delivery and duplicate protection
are not guaranteed. Applications requiring ordered reliable delivery of
streams of data should use the Transmission Control Protocol (TCP).
2)