The hour is a unit of time measurement equal to 60 minutes or 3600 seconds. It is 1/24 of a median Earth day. An hour's duration can vary slightly for time standard adjustment purposes, ranging from 3599 to 3601 seconds in Universal Coordinated Time. The word "hour" derives from the Latin "hora" and Greek "hōra," originally meaning "season." It entered Middle English in the 13th century through Old French.