UDP is a simpler data based connectionless protocol compared to the TCP (Transmission Control Protocol). In connectionless protocols, there is no attempt made to create a dedicated one-to-one connection. Communication is achieved by transmitting information in one direction, from the source to the destination without monitoring if the destination is online, or if it is ready to receive the data. With UDP, data packets cross the network as independent units; as a result, UDP is not at all reliable compared to the TCP. Packets are sent individually and will always be whole when they arrive. Packets have definite limits and no splitting or merging of data occurs. The data may arrive out of order, appear duplicated, or go missing without notice. There is no verifying mechanism to check every packet if it has actually arrived and there is no proper arrangement of messages, no monitoring connections, etc, which makes UDP faster and more efficient for small amounts of data. Programs often use UDP because dropped packets are preferable to delayed packets. UDP's connectionless nature is very useful for servers that have to answer a large number of small queries. Unlike TCP, UDP can perform packet broadcasts (sending to all clients on the network) and multicasting.

Some programs that use UDP are: the Domain Name System (DNS), streaming media (IPTV, VoIP), and online games.

UDP uses network ports for application-to-application communication. UDP port numbers range between 0 and 65,535. Port 0 is used only for sending data that does not expect a response.