What does SID stand for?

• A. Secure Identity Descriptor
• B. System Identification
• C. Service Identifier
• D. System Identifier

Answer: (D)

SID stands for Security Identifier, the unique value Windows assigns to every security principal—users, groups, and computer accounts. This identifier is what the system uses to enforce permissions in access control lists. Even if a user changes their display name or profile, their SID stays the same, ensuring persistent and accurate security rights. SIDs have a distinctive format that begins with S-1-..., and the final part (the RID) differentiates individual accounts or groups within a domain or local machine.

The other options aren’t standard terms used in Windows security. Secure Identity Descriptor, System Identification, or Service Identifier aren’t the recognized meaning of SID in this context, and would not be used to refer to the mechanism that controls access permissions.