A checklist in the National Checklist Repository that is considered production-ready and has been validated by NIST or a NIST-recognized authoritative entity to ensure, to the maximum extent possible, interoperability with SCAP-validated products. Tier IV checklists also demonstrate the ability to map low-level security settings (for example, standardized identifiers for individual security configuration issues) to high -level security requirements as represented in various security frameworks (e.g., SP 800-53 controls for FISMA), and the mappings have been vetted with the appropriate authority.
Sources:
NISTIR 7511 Rev. 4