From Wikipedia..."ASP.NET is an open-source[2] server-side web application framework designed for web development to produce dynamic web pages. It was developed by Microsoft to allow programmers to build dynamic web sites, web applications and web services."

From Ross...Aspx is a used in conjunction with C# to create applications using the Visual Studio development environment. Aspx provides the developer with access to a large array of tools and controls to build useful and efficient applications hosted in a windows, IIS and SharePoint environments.