mixed mode

mixed mode: In a Windows 2000 domain, the default domain mode setting. Mixed mode enables Windows NT-based backup domain controllers to coexist with Windows 2000-based domain controllers. Mixed mode does not support universal groups or the nesting of groups. You can change the domain mode setting to native mode when all Windows NT-based domain controllers are removed from a domain.

In Windows Server 2003 domains, mixed mode is referred to as Windows 2000 mixed, and it is one of three domain functional levels available.