ASPX, Active Server Page Extended File (.aspx)
The ASPX Website file format
The file extension ASPX are used for automatically or server-generated web pages that lead to an active server. They are commonly associated with the Microsoft ASP.NET framework and can be created using Microsoft's Visual Web Developer program. This website format file can be opened in any web browser if the URL ends with the ASPX extension, i.e. ".aspx".
Technical details of ASPX files
These files also known as ".NET web forms" may contain VBscript, code written in C#, or XHTML markup. Dynamic code is supported by this web form format as well. The scripts and command contained in the file are processed on a web server which sends the contents to a user's browser in proper HTML format. With the release of ASP.NET Framework 2.0 it is possible to split ASPX files into pages that contain static text only (ASPX) and files that contain the dynamic code (e.g. ASPX.VB).