UDP - Definition from the Hotspot Shield Glossary
User Datagram Protocol is a datagram communications protocol that is meant to be used as an alternative to TCP (Transmission Control Protocol).
Its main use is for creating low loss and latency tolerating connections between devices on the internet. UPD offers additional functionality to the IP layer as it helps distinguish user requests by identifying port numbers, and a checking feature to ensure that the data has arrived as intended. While TPC checks all packets and re-sends packets that have been lost, UDP simply sends the packets and that’s it. This means that UDP provides a quicker transmission with lower bandwidth usage, however it can also mean that data can be lost or corrupted. This protocol resides in the Transport Layer of the OSI reference model and is used with higher level protocols like TFTP, RTSP and SNP.