week

A week is a time unit equal to seven days. It is the standard time period used for cycles of rest days in most parts of the world, mostly alongside—although not strictly part of—the Gregorian calendar.
The days of the week were named after the classical planets (derived from the astrological system of planetary hours) in the Roman era. In English, the names are Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday .
ISO 8601 includes the ISO week date system, a numbering system for weeks within a given year – each week begins on a Monday and is associated with the year that contains that week's Thursday (so that if a year starts in a long weekend Friday–Sunday, week number one of the year will start after that). ISO 8601 assigns numbers to the days of the week, running from 1 to 7 for Monday through to Sunday.

The term "week" is sometimes expanded to refer to other time units comprising a few days, such as the nundinal cycle of the ancient Roman calendar, the "work week", or "school week" referring only to the days spent on those activities.

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