What is User Datagram Protocol (UDP)?

What will be an ideal response?

This protocol is similar to TCP in that it handles the
addressing of a message. UDP breaks a message into numbered segments so that it can
be transmitted. It then reassembles the message when it reaches the destination computer.
Unlike TCP, UDP is connectionless: it simply sends segments of messages without
performing error-checking or waiting for an acknowledgment that the message has
been received. Such a protocol is useful for video and audio broadcasts on the Internet.
TCP and UDP are often mentioned together in discussions of firewalls because
both transmit data through ports and thus open up vulnerabilities. It's useful to set up
rules to block UDP traffic on all ports 21 and below so as to block traffic on ports
that control hardware and are not part of the routed network environment.