The Windows Insider Program is a Microsoft initiative that allows users to sign up and test pre-release versions of the Windows operating system. Participants, known as 'Insiders,' get early access to new features, updates, and improvements before they are officially released to the general public. By providing feedback and reporting bugs, Insiders help Microsoft identify issues and improve the final product. The program is open to anyone with a compatible device and a Microsoft account, making it a collaborative effort between Microsoft and the community to enhance Windows.