Microsoft .NET Core is an open-source, cross-platform framework designed for building applications that can run on various operating systems, including Windows, macOS, and Linux. It allows developers to create web applications, services, and console applications using languages like C# and F#. One of the key features of .NET Core is its modular architecture, which enables developers to include only the necessary components for their applications, making them lightweight and efficient. Additionally, it supports modern development practices, such as microservices and cloud-based applications, enhancing flexibility and scalability for developers and businesses alike.