ASPX (Active Server Pages Extended) is a file extension for web pages generated by Microsoft's ASP.NET web framework. These files contain a combination of HTML, server-side code (typically C# or VB.NET), and client-side scripting (JavaScript, CSS). When a user requests an ASPX page, the web server processes the server-side code, which can interact with databases, perform calculations, and dynamically generate HTML content. This dynamically generated HTML is then sent to the user's browser for rendering. ASPX files are a core component of building dynamic and interactive web applications. They enable developers to create complex web pages with features like user authentication, data management, and personalized content. The ASP.NET framework provides a robust environment for developing and deploying ASPX-based web applications, offering features like security, scalability, and maintainability. ASPX pages are typically hosted on web servers running the .NET framework, such as Internet Information Services (IIS).