ASP.NET is a web development platform, which provides a programming model, a comprehensive software infrastructure and various services required to build up robust web sites with HTML, CSS, JavaScript and server scripting.
ASP.NET is a part of Microsoft .Net platform. ASP.NET applications are compiled codes, written using the extensible and reusable components or objects present in .Net framework. When a browser requests an ASP.NET file, the ASP.NET engine reads the file, compiles and executes the scripts in the file, and returns the result to the browser as plain HTML.
It consists of a large number of controls such as text boxes, buttons, and labels for assembling, configuring, and manipulating code to create web sites using HTML pages.