In a windows network, the server is called what?

domain controller

Depends on what it does. If it shares the Internet between multiple computers within the network, then it's a domain controller.

A database server is just the server that contains and controls the database of the network.

Web servers handle web sites. When you go on any website, you're directly making a connection to the site's web server.

File servers just host the files for the people of the network and/or the web server, if the website is a file hosting service, etc.

the answer to your question is Domain Controller

a Database server is just that a server that holds a database of information

A web server runs a program that allows web browsers to see web pages loaded on that server

a file server is a computer with a larger hard drive where people allover the office can store files

"Server" is a generic term for a machine that is providing a "service" to a domain or network.

Thus, a Primary Domain Controller is a server just like a SQL server is a server.

Most commonly, either the Domain Controller, Exchange server, or file server are often referred to as "the server."