INOP
Inoperative. INOP means a system, component, or function is inoperative or unavailable for normal use.
Expanded explanation
INOP signals unavailable functionality with operational consequences
INOP is common in technical and operational contexts where systems, components, or functions are unavailable but still must be recorded, evaluated, and handled correctly. The shorthand is compact, but the operational implication can be significant.
Why it matters
INOP is a strong example of safety-critical shorthand. It shows why glossary pages can do more than define terms: they can explain why the term matters inside real aviation workflows.