ASP.NET is an open-source, server-side, web-based technology developed by Microsoft. It’s a key part of its .NET framework, acting as an extension that specifically allows developers to build web applications and services. Much like .NET, it support a number of programming languages, like C# and Visual Basic. Also, being part of the .NET Framework, it utilizes the Common Language Runtime (CLR), which, by compiling code into an intermediate state, can load and upload pages quickly. This makes ASP.NET a good choice for performant sites and applications which have dynamic pages.
The latest versions of ASP.NET are called ASP.NET Core, which is cross-platform and can be used to develop applications for a number of operating systems, instead of just Windows.