Lapse is a singular noun. The plural is lapses. A lapse of time is a length of time, usually used to indicate the amount of time that something happened differently than before, or the space of time between two events. The adjective “time-lapse” is used to describe a video or a series of still photographs in which some of the sequence is removed. This allows a slow process to be viewed more quickly. To time laps is to record how long it takes to move around the track.