ASPX stands for Active Server Page Extended File, and it is developed by Microsoft. It is a type of ASP.NET Web file that can feature business logic, Web controls and presentation.
Also referred to as .NET webforms, ASPX pages are usually written by Microsoft Visual Web Developer and are intended to work in the ASP.NET framework. This means that the scripts of the page run in the Web server, and the resulting HTML is conveyed to the browser of the user. A good example of ASPX filename is "Default.aspx." Web pages are contained in files with the .aspx extension. These files typically feature static HTML markup, where developers insert the content for the Web page.