means A precise moment in time, or something that happens or is available immediately with no waiting.

from From Latin 'instans,' the present participle of 'instare' — to stand upon, to press close, to be at hand — built from 'in-' (upon) plus 'stare' (to stand). The image is of a thing standing right over you, urgently near. It entered English through Old French in the late Middle Ages, first meaning 'pressing' or 'urgent' (a sense surviving in 'instant need'), then narrowing to the razor-thin slice of now. The grocery-shelf sense — instant coffee, instant pudding — is a 20th-century arrival, when 'standing close at hand' became a selling point.