Time is explained.
Time measures events of past, present and future in time period or at point of time.
Time can be measure in seconds, minutes, hours, weeks, months or years etc. The basic unit of time is second. Its symbol is s. Larger units of time are minutes (min) and hour (h).
Periodic events are those events which happen after some time and repeated again and again. Periodic events (sun rise and sun set for a day etc.) are used for the measurement of time. Periodic motion of a pendulum has been used to make clocks and watches.