duties of individuals requiring separation

This is a compositional phrase, not a term of art. In NIST SP 800-53 AC-5, it appears inside an organization-defined assignment parameter: "Identify and document [Assignment: organization-defined duties of individuals requiring separation]." The phrase simply names the object of that assignment — the set of role-based responsibilities an organization must enumerate before it can enforce separation of duties — and its meaning is fully assembled from its ordinary parts. The two-step operational expectation is to "identify the duties of individuals requiring separation" and then "define system access authorizations to support separation of duties," making plain that the phrase is a procedural instruction, not a coined concept.