Security Identifier

Identifier used for user accounts and groups in Microsoft Windows

In the context of the Microsoft Windows NT line of operating systems, a Security Identifier (SID) is a unique, immutable identifier of a user, user group, or other security principal. A security principal has a single SID for life, and all properties of the principal, including its name, are associated with the SID. This design allows a principal to be renamed without affecting the security attributes of objects that refer to the principal.

This keyword could refer to multiple things. Here are some suggestions: