What is a Servant and Master ?
The same thing as a Server and Client.
a Servant would hopefully refuse a command to kill a human being,
So also will a Server refuse to do tasks it hasn't been authorised to do.
A server is normally a Computer System that is always connected to
the Internet. It Normally provides some form of service eg.
E-Mail, Webpages, Time, DNS, Irc, Mud and many many other services.

a Client is a computer system connecting to a Server and asking it to
provide a service.
eg. If you are using Internet Exploder to ask a Webserver like Apache
for some pages the Internet Exploder is the Client and the Apache is the Server.
You can also have your own servers on the Internet click here : 999