SSH stands for secure shell. It looks like telnet.

The main  difference between SSH and Telnet is that SSH 
transparently encrypts the data between the client and the 
server.

When you telnet to a router/switch/firewall/etc then it 
say, type your password, every keypress of your password is 
transfred  across the Internet to our server in cleartext. 
This means that if some  person on one of the routers 
through which the information passes sniffed the packets  
then they'had suddenly know your password, letter for 
letter!

With SSH, the information is encrypted. So when you type 
your password, each letter is "scrambled" before it's sent 
over the Internet, and decoded at the other end. The 
encryption method is such that, if someone in between the 
servers stumbled upon the information, they'd just see a 
jumbled noise.

As you might imagine, this increases your security 
significantly.

By default, SSH uses port 22 and telnet uses port 23

ton of thanks to you for that brilliant answer because i was searching for that answer i read it from tenon bom and frozen but didn't get what they want to say.

sweta Singh

b.tech 3rd yr

Jeetu u missed 1 thing which u told me that day..
SSH uses 3-way handshaking, whereas telnet uses simple snmp
for communicating

telnet is a remote management protocol
ssh is the same but secure
SSH sends your login and password (and everything else) 
converted into secret code that gets unencoded at the other 
end. That way anyone that is sniffing one of the systems 
involved cannot see and steal your password.

However, because SSH is encrypted it is not appropriate for 
some uses. Where speed is needed, or over really bad slow 
connections, or when a raw connection is needed. For 
example, system administrators often use telnet to 
troubleshoot other services such as webserver or email 
because they can see exactly what is and is not getting sent 
and received.

Also telnet is easier to include into other programs so in 
cases where security is not a big deal, telnet will often be 
used. Such as online games.