individuals requiring separation

No definition is given in NIST SP 800-171r3. The term is attested in use at 1 citation in that document; a definition is pending curation.

A compositional noun phrase, not a term of art. It describes, within the context of a separation-of-duties control, the personnel whose assigned roles or functions have been identified as needing to be divided across different people — i.e., those whose combined access to authorization, execution, recording, or audit functions would create an unacceptable conflict or fraud risk. Separation of duties addresses the potential for abuse of authorized privileges and reduces the risk of malevolent activity without collusion, including dividing mission functions and support functions among different individuals or roles and ensuring that those who administer access control functions do not also administer audit functions. The phrase appears as part of an assessment objective — "the duties of individuals requiring separation to reduce the risk of malevolent activity are defined" — where it modifies "duties" and simply points to whichever personnel hold roles that, per policy, must not be held by the same person.