User Datagram Protocol over Internet Protocol.
UDP is a “connectionless” protocol
UDP has no explicit provision for acknowledgement of packets received.
(Sometimes mistakenly called unreliable datagram protocol).
UDP is connection less data transfer, it means there will not be any handshake between peers. Server will listen at some port and accept the packet to the port from any client.
Unreliable data transfer, there is no acknowledge for data.
UDP packet may take any path to reach the destination. So there is a possibility of duplicate packets to reach the destination. It will take the first packet and discard the duplicates.
Packet ordering is not important for UDP, it will accept packets in any order finally it will rearrange by it packet sequence number.
UDP is much faster than TCP.
It is always recommended that UDP is used of small data transfers. UDP are used to get the Network management statistical detail from SNMP Agents or get the IP address from the DNS
Server giving Host Name. UDP packets are low priority packets in the network.