Server and Client
An Internet services is based on a protocol
established between a Server and a Client.
Servers and clients are both programs, where
one of each type runs on the two machines that
are to be connected.
Servers run permanently as so called daemons
and wait for a request of client.
For example a http daemon (httpd),
usually an Apache server, waits for the request of
a web page from a browsers (Netscape, etc).