Source: https://www.cloudflare.com/learning/ddos/glossary/user-datagram-protocol-udp/

====== UDP ======

User Datagram Protocol is a [[network-layer_transport|layer 4]] connectionless communication protocol for time-sensitive transmissions. It does not establish connections nor does it keep track of what it sent and how successfully.

UDP is faster but less reliable than [[tcp|TCP]]. 

{{ :tcp-vs-udp.svg |}}

It's used in [[DNS|DNS]] lookups or in Network Time Protocols (since the queries are very simple), RIP, DHCP and so on.