Telnet is a tool to open a terminal (text console) connection to another machine. The average joe won't have much use for this but there are rare times (when testing a mail server for instance, checking firewall setups, etc) when you may need it. Annoyingly it was removed from Windows Vista and Windows 7 by default but thankfully it can be reinstalled with a few simple steps.
- Click Start
- Click Control Panel
- Select Programs And Features
- Select Turn Windows features On or Off
- Tick Telnet Client
- Click OK
Once it has installed you will be able to use Telnet from the command prompt or the run command, the same as you could with Windows XP and 2000.