أَيْنَ الْمَفَاتِيحُ؟ فِي الدُّرْجِ.
Where are the keys? In the drawer.
The answer omits the full clause “the keys are in the drawer.” The question supplies a clear contextual cue from which the listener recovers the intended proposition.
This is useful ellipsis because the unspoken part is recoverable. If its recovery is impossible and the sense breaks down, brevity becomes defective rather than eloquent.