More precisely called «object class», a logical grouping of objects within Active Directory in Microsoft Windows 2000. Objects are organized within Active Directory by their classes. Examples of object classes can include users, groups, computers, domains, and organizational units (OUs). Each class of objects has its own defining properties or attributes, as laid out in the Active Directory schema. Grouping objects logically into classes makes it easier to find and access these resources on the network.
Active Directory comes with predefined object classes. You can create additional classes or modify existing ones using the Active Directory Schema.