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.

TCP is a connection oriented protocol, which means that 
everytime a packet is sent say from host A to B, we will 
get an acknowledgement. Whereas UDP on the other hand, is a 
connection less protocol.
Where will it be used : TCP -> Say you have a file transfer 
and you need to ensure that the file reaches intact, and 
time is not a factor, in such a case we can use TCP.

For more details : http://newadmins.blogspot.com/

TCP is a Transmission Control Protocol. 
UDP is a User Datagram Protocol.
TCP protocol is mainly used when we need report that our
data has trasferred succesfully or not,
while UDP doesnot check

1.	TCP(Transmission Control Protocol). TCP is a 
connection-oriented protocol, a connection can be made from 
client to server, and from then on any data can be sent 
along that connection. 
o	Reliable - when you send a message along a TCP 
socket, you know it will get there unless the connection 
fails completely. If it gets lost along the way, the server 
will re-request the lost part. This means complete 
integrity, things don't get corrupted. 
o	Ordered - if you send two messages along a 
connection, one after the other, you know the first message 
will get there first. You don't have to worry about data 
arriving in the wrong order. 
o	Heavyweight - when the low level parts of the 
TCP "stream" arrive in the wrong order, resend requests 
have to be sent, and all the out of sequence parts have to 
be put back together, so requires a bit of work to piece 
together. 
2.	UDP(User Datagram Protocol). A simpler message-
based connectionless protocol. With UDP you send messages
(packets) across the network in chunks. 
o	Unreliable - When you send a message, you don't 
know if it'll get there, it could get lost on the way. 
o	Not ordered - If you send two messages out, you 
don't know what order they'll arrive in. 
o	Lightweight - No ordering of messages, no tracking 
connections, etc. It's just fire and forget! This means 
it's a lot quicker, and the network card / OS have to do 
very little work to translate the data back from the 
packets.

1.tcp is connection oriented udp is connectionless
tcp is reliable udp is not;