计时 literally means 'to calculate time' — 计 (jì) means 'to calculate, to measure, or to plan', and 时 (shí) means 'time'. Together, they form a verb meaning 'to time' — that is, to measure the duration of an event using a clock, stopwatch, or other timing device. It is commonly used in contexts involving sports, experiments, competitions, or any activity where precise measurement of elapsed time matters.

This word is neutral in register and widely used in both spoken and written Chinese. While it can appear as a noun ('timing' or 'a timing session'), its primary function is verbal — for example, in commands like '请开始计时' (Please start timing) or descriptions like '教练正在为运动员计时' (The coach is timing the athletes). It does not imply estimation or approximation; it specifically refers to objective, instrument-assisted time measurement.