Plain English Meaning
The instrument shows what is happening right now, the moment it happens, without delay.
Full Definition
An instrument display that responds to a change immediately as it happens, showing the current value in real time without lag, averaging, or trend smoothing.
Context Anchor
Seen in instrument flying when choosing which cockpit display gives the best immediate cue for power changes.
Derivation
From Latin instans meaning 'present moment.' An instantaneous indication is one that reflects the present moment, not a delayed or averaged reading.
Why Pilots Care
Allows timely recognition of power changes so the pilot can make precise adjustments without waiting for a lagged instrument to stabilize.