ASPX / ASP.NET – Active Server Page Extended
ASP.NET is a part of the .NET framework, marketed by Microsoft, used to write programs and design web forms using Common Language Runtime (CLR) and a huge class library of Multiple Languages. The most commonly used languages in .NET are VB and C#. A web form has an extension of “aspx”.
ASP.NET processes all code on the server and returns the resultant HTML to the client. Microsoft has created an amazingly well designed MSDN library for ASP.NET and all of the other .NET languages.