Time. Time is a human perception defined as the length of an interval separating two points on a nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future. The intervals are measured in seconds, minutes, hours, days, years.
Second. A second is a unit of time equal to one sixtieth of a minute.
Minute. A minute is a unit of time equal to 60 seconds. It is one sixtieth of an hour.
Hour. An hour is an interval of 60 minutes. It is one of 24 equal parts of a day.
Day. A day is the 24-hour period during which Earth completes one rotation on its axis.
Year. A year is the period of time during which Earth completes a single revolution around the Sun. It amounts to 365 days, 5 hours, 49 minutes, and 12 seconds of mean solar time. In the Gregorian calendar we use, the year begins on January 1 and ends on December 31. It is divided into 12 months, 52 weeks, and either 365 or 366 days, depending upon the Leap Year rule. The interval also is known as a calendar year.