Microsoft Defender is a security solution that is focused on protecting endpoints, such as desktops, laptops, and servers. It includes features such as antivirus, firewall, and endpoint detection and response (EDR) capabilities. Microsoft Defender is available for Windows 10, Windows Server, and macOS.

Microsoft 365 Defender, on the other hand, is a more comprehensive security solution that is designed to protect the entire Microsoft 365 environment, including endpoints, email, identities, and applications. It includes features such as endpoint protection, email protection, identity protection, and cloud application security. Microsoft 365 Defender is a cloud-based solution that is integrated with other Microsoft 365 services, such as Azure Active Directory and Microsoft Cloud App Security.