ASP is "Active Server Pages," a server-side scripting environment that was created by Microsoft in 1996, and released as part of IIS 3.0 (ASP 2.0 was released in conjunction with IIS 4.0, and ASP 3.0 was released in conjunction with IIS 5.0). ASP is used to create and run dynamically created or interactive web server applications, and since version 2.0 has provided six built-in objects: Application, ASPError, Request, Response, Server, and Session.
In 2002, ASP.NET was released, which was meant to replace ASP for most uses. ASP is still supported on IIS on Windows Servers though, so it has become known as "Classic ASP" by many in the development community.