ASP.NET Core is an open-source web framework developed by Microsoft for building modern web applications and services. It allows developers to create dynamic websites, APIs, and cloud-based applications using the C# programming language. The framework is designed to be cross-platform, meaning it can run on Windows, macOS, and Linux. One of the key features of ASP.NET Core is its modular architecture, which enables developers to include only the necessary components for their applications. This results in improved performance and easier maintenance. Additionally, it supports dependency injection, making it easier to manage code and promote reusable components.