Answer
ASP.NET Core is a modern, high-performance, cross-platform framework for building web applications and APIs that can run on Windows, Linux, and macOS.
It was created to overcome limitations of the old ASP.NET Framework such as heavy runtime dependency on the full .NET Framework, tight coupling to IIS, poor modularity, and difficulty integrating with modern CI/CD and containerized environments.
ASP.NET Core introduces a lightweight runtime, a fully modular component system, built-in dependency injection, a unified hosting model, and a redesigned request pipeline focused on speed, flexibility, and cloud readiness.