TCP is a Transmission Control Protocol. 
UDP is a User Datagram Protocol.
There are four major differences between UDP and TCP:
1. TCP can establishes a Connection and UDP cannot.
2. TCP provides a stream of unlimited length, UDP sends 
small packets.
3.TCP gurantees that as long as you have a connection data 
sent will arrive at the destination, UDP provides not 
guarantee delivery.
4.UDP is faster for sending small amounts of data since no 
connection setup is required, the data can be sent in less 
time then it takes for TCP to establish a connection.