Web Server

The term "web server" sometimes refers to a server computer and sometimes to the web server software that runs on a server computer.

The purpose of web server software is to receive and respond to requests for web pages from a web browser running on a client machine.

When the web server receives a request, it often needs to simply send back a "static" web page.  Sometimes, however, it must invoke server-side scripts or application system that reside on a different server).

This "logic" must then obtain the requested data and insert the formatted information into a dynamically built web page.

World Wide Web - Conceptual Overview

There are many different types of web server software. The operating system (e.g. Unix, Linix, Windows, etc) on the server computer determines what type of web server software can run.

For example, on Windows computers, IIS (Internet Information Server) server software is often used.  On Linux machines, Apache web server software is commonly used.