Week

A week is a period of seven consecutive days. Its starting day varies by calendar, culture, and convention.

Day: A day is a unit of time defined by Earth's rotation or by a calendar convention. Seven consecutive days make up a week.
Babylonian calendar: The Babylonian calendar was a lunisolar system used in ancient Mesopotamia. Mesopotamian practices helped establish seven-day time divisions.
Workweek: A workweek is a recurring span of days designated for ordinary employment. It turns the week into a standard unit for labor schedules.
ISO week date: ISO week date is a calendar system that numbers weeks and assigns them to years using standardized rules. It specifies Monday as the week's first day and defines week numbering precisely.
Calendar: A calendar is a system for organizing time into days, months, years, or other intervals. Calendars place weeks within larger systems of dates.
Sabbath: The Sabbath is a recurring day of rest and religious observance in Judaism and other traditions. The Jewish Sabbath anchored a recurring seven-day cycle.
Weekly calendar: A weekly calendar displays days in repeating seven-day rows or cycles. It makes the week a practical framework for planning appointments and tasks.
Lunar month: A lunar month is the interval between successive corresponding phases of the Moon, averaging about 29.5 days. Its length does not align exactly with a whole number of weeks.
Seven-day week: The seven-day week is a recurring cycle used to organize time independently of months and years. It is the specific recurring pattern described by the word week.
Planetary week: The planetary week assigns each day to one of the seven classical planets in sequence. This ancient naming tradition shaped the names of weekdays in several languages.

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