Windows Defender is a built-in antivirus and anti-malware program included with the Windows operating system. It helps protect your computer from viruses, spyware, and other malicious software by scanning files and applications in real-time. It also provides regular updates to ensure it can defend against the latest threats. In addition to virus protection, Windows Defender includes features like a firewall, which monitors incoming and outgoing network traffic, and a security dashboard that gives users an overview of their system's health. Overall, it aims to provide a comprehensive security solution for Windows users.