So just what is a "Server" anyway?

At its simplest, a "server" is nothing more than a computer that provides services or resources to other computers. In that sense there's nothing very special about being a server. In fact, if your machine is has file sharing enabled and others are able to copy files to and from your machine then your machine is a file server.

Things get confusing because the general term "server" is often used to mean a machine optimized for a particular purpose.

For example your machine may be a file server but is it a good file server? Is it optimized to provide fast access to lots of files to hundreds or thousands of other computers? Probably not. But there most certainly are machines that are optimized to be extraordinarily efficient at exactly that. They may even look and operate just like your own computer but perhaps have high speed network connections, extremely fast hard disks, multiple processors and more, all to make them good at what they do. And the things that don't matter like video or sound hardware might be bare bones, if present at all.

They may be called "file servers", but really they're just computers with a specialty.

So your ISP's mail server is just a computer optimized to handle email. That might mean it has lots of disk space for all the spam. It could mean that it has redundant components to reduce the possibility of lost email as a result of catastrophic failure. It almost certainly means it has an efficient connection to the internet.

A print server? It's just a computer optimized for printing. It probably has lots of disk space for spooled print files. Printing is a somewhat slow operation so maybe the disks themselves need not be as fast as a file server's. If it serves up multiple printers then it needs enough parallel printer ports, USB connections, or what have you to actually communicate with each printer.

Web servers? Since web access is really just a form of file access, web servers might look a lot like file servers. Large fast hard disks, good network connections, and so on.

What about "dedicated" or "shared"? It's commonly used these days when discussing Web Hosting. You can host your web site on a machine shared with many others or on a machine dedicated to just you. It depends on your needs. But the same terms apply elsewhere; for example I have an older PC that I use as a print server - it's shared because it's accessible to all the other machines on my network.

So what's a "server"? In a sense there's really no such thing as just a "server". There's always some type of resource that's being served which is either explicit or implied. A server is just a computer that's been selected and probably optimized to perform a specific task in service to others and it's that task that makes all the difference.