.NET is a free, cross-platform, open-source development platform that can be used to build many different types of applications. .NET Core and .NET Framework are two implementations of the .NET platform.
.NET Framework is the original implementation of .NET introduced in . It is a mature development framework that supports running websites, services, desktop apps, and more on Windows.
.NET Core, on the other hand, is a more recent open-source .NET platform, introduced in 2016, that allows you to build cross-platform applications, e.g., for Windows, Linux, and macOS.
.NET Core was built as an open-source alternative to the Windows-specific .NET Framework. .NET Core started as a subset of the .NET Framework, but soon, more APIs were added and it is now the preferred choice for development.
However, all new feature APIs will go to .NET Core; so, Microsoft recommends that developers shift to .NET Core to develop new applications in order to use the latest language features and runtime improvements.