duration

Duration is the length of time during which something occurs or exists. It is the elapsed time from the beginning to the end of an event, and is measured with clocks and timers. The second is the basic SI unit for duration; common units include minutes, hours, and days.

An interval is a span of time with clearly defined endpoints, while duration is the amount of time contained within that interval. For example, the duration of a meeting is how long it lasts.

Different fields use the concept of duration in distinct ways. In music, duration refers to how long a note or rest lasts. In film, video, and live performance, it describes how long a scene or act runs. In computing and telecommunications, a duration can specify the length of a delay, timeout, or timer.

Perceived duration can differ from clock time. Attention, emotion, and arousal can make intervals feel longer or shorter, a phenomenon studied in psychology and neuroscience.

In physics, duration relates to elapsed or proper time—the time measured by a clock along a specific path. In relativity, observers in relative motion may measure different durations for the same event, highlighting the relative nature of time.

In planning and project management, duration is the total time required to complete a task or activity, including scheduling constraints. Accurate estimation of duration supports timelines, resource allocation, and risk assessment.

See also: timespan, interval, latency, delay.