U

universal group

A universal group can appear in access-control lists (ACLs) anywhere in the forest, and can contain other universal groups, global groups, and users from anywhere in the forest. Enterprises with a single domain should not use universal groups. Typically, the members of a universal group are global groups rather than individual users. See What Type of Group to Use.

update sequence number (USN)

An update sequence number is a 64-bit number that each Active Directory™ server maintains to indicate the sequence of changes on the local DC. Each DC increments its USN whenever it modifies a directory object. The DC assigns the incremented USN to the uSNChanged attribute of the object that changed. The uSNChanged attribute is not replicated, so an object's uSNChanged value can be different on different DCs.

user principal name (UPN)

A user principal name is a "friendly" name for a user or group, shorter than the distinguished name, and easier to remember. It is composed of a shorthand name for the user and the domain name service (DNS) name of the tree where the user object resides. For example, someone in the microsoft.com tree might have the UPN someone@microsoft.com.