The default page displayed in Microsoft's Internet Information Services (IIS), default.asp is designed to replace index.html.

Whenever you visit a website, such as www.everything2.com, the web server running on the system must display a specific file. Since it's easier for people to remember yahoo.com or everything2.com than it is for people to remember yahoo.com/index.html or everything2.com/index.pl, the web server is coded so that a specific file can be used as the default document, so when people type just the domain name, or the domain name and a directory (yahoo.com/homer/), they'll be shown the default document instead of a "404 File Not Found" error.

Microsoft's IIS (as of version 4.0, at least), which comes stock with Windows NT 4, Windows 2000, Windows XP Professional, and Windows Server 2003, and Microsoft's Personal Web Server (PWS), which comes with Windows 95, 98, and Me, both use either default.htm or default.asp, which is user-definable, instead of the traditional index.html. Though I'm not certain why they chose to use default as the file name (aside from the fact that it sounds cooler, and in this industry you must sound cool to be cool), the .asp extension stands for Active Server Page.

Active Server Pages are Microsoft's semi-proprietary format for server-side scripting, and can be written in JScript, VBScript, and ASP.net.