Plain English Meaning
An engine gauge is showing a reading that is too high, too low, or otherwise not normal, suggesting something may be wrong with the engine.
Full Definition
An engine instrument reading that falls outside the normal operating range published by the manufacturer, signaling that one or more engine parameters — such as oil pressure, oil temperature, cylinder head temperature, fuel flow, fuel pressure, manifold pressure, or RPM — is no longer behaving as expected and may indicate a developing or active engine problem.
Context Anchor
A pilot may notice this while checking engine gauges before takeoff, during climb, in , during , or any time an engine warning or gauge reading changes unexpectedly.