NuGet Package Manager is a tool used in software development to manage libraries and dependencies in projects, particularly those built on the Microsoft .NET platform. It simplifies the process of adding, updating, and removing packages, which are collections of reusable code that developers can use to enhance their applications without having to write everything from scratch. With NuGet, developers can easily search for packages from a vast online repository, ensuring they have access to the latest versions and features. This tool integrates seamlessly with development environments like Visual Studio, making it user-friendly and efficient for managing project dependencies.