In physics and the philosophy of science, instant refers to an infinitesimal interval in time, whose passage is instantaneous. In ordinary speech, an instant has been defined as “a point or very short space of time,” a notion deriving from its etymological source, the Latin verb instare, from in- + stare (‘to stand’), meaning ‘to stand upon or near.’ As of October 2020, the smallest time interval certify in regulated measurements is on the order of 397 zeptoseconds (397 × 10−21 seconds).