I been hearing the term "server crash" for as long as I can remember, but I have no idea about what that physically means. Can anyone fill me in?

It means anything from a unexpected lock up / reboot to the hardware blowing up.

I think Chris hit it on the head, because the term "server" refers to the software, such as Apache, that may become unstable just like a sound editor or word processor may freeze up.

The term "server" also refers to the hardware (computer) which is dedicated to doing nothing but run the server software and other related essentials, such as firewall, antivirus and script engines. Hardware failure may occur.

In either case, the web site is off the air.