.NET is a software framework developed by Microsoft that allows developers to create a wide range of applications, including desktop, web, mobile, and gaming applications. It provides a common language runtime (CLR) and a class library that developers can use to write code in different programming languages such as C#, F#, and Visual Basic. .NET Core, on the other hand, is an open-source, cross-platform implementation of the .NET framework. It is designed to run on Windows, Linux, and macOS and provides a smaller, more modular runtime that allows developers to build and deploy applications more efficiently. It also includes a set of libraries and tools for building web and cloud-based applications.