Entity

NIST SP 800-27rA

Either a subject (an active element that operates on information or the system state) or an object (a passive element that contains or receives information).

NIST SP 800-33

Either a subject (an active element that operates on information or the system state) or an object (a passive element that contains or receives information).

NIST SP 800-57P1

An individual (person), organization, device or process.

NIST SP 800-89

An individual (person), organization, device or process. Used interchangeably with "party".