User Datagram Protocol
The TCP/IP protocol that allows packets of data, or datagrams, to be sent from one Internet application to another.
UDP is a “connectionless” protocol, because, unlike TCP, it does not require the sender and receiver to establish a connection before data is transmitted.
It’’s considered “unreliable,” because it doesn’’t guarantee that datagrams will arrive in the same order they were sent, or even that they will arrive at all.
If reliability is desired, it’’s up to the application using UDP to provide it.