The document discusses different types of web servers. It explains that a web server is a program that uses HTTP to serve web pages in response to user requests. It then describes some major web server types: Apache, which is open source and runs on many operating systems and has about 60% market share; IIS, which is Microsoft's proprietary web server that runs on Windows; Nginx, an open-source alternative to Apache known for performance; and Sun Java System Web Server, suitable for medium and large sites but not open source.