Who this is for: Auditors.
Every nonconformity is recorded as either Major or Minor.
Major nonconformity — the requirement has broken down rather than slipped. Typically one of:
A required process does not exist at all.
A process exists but has failed completely, or across the board rather than in one instance.
The failure has caused, or could plausibly cause, harm, a regulatory breach or a failed certification.
Several minor nonconformities in the same area that together show the system is not working.
Minor nonconformity — the process exists and generally works, but a single instance or a small number of instances fall short. An isolated missing record, one out-of-date document, one person who has not had a refresher.
Severity matters practically as well as descriptively. Your organisation can require closure verification on major nonconformities but not on observations, which means a major NC cannot be closed until someone independent has checked the corrective action actually worked.