Week

A week is a unit of time equal to seven days, serving as the standard calendrical period between a day and a month in most parts of the world. There are just over 52 weeks in a year. The days of the week are commonly used to designate work days, rest days, and holy days. The term "week" can also refer to sub-sections like the workweek and weekend, and certain weeks may be designated for a particular purpose, such as Golden Week in China and Japan, or awareness weeks like National Family Week in Canada.

Pre-modern

Historically, week lengths varied across cultures. Ancient Egypt used a ten-day week, the Etruscans and early Romans an eight-day week, and some modern West African cultures have four- or five-day market weeks. The Romans later adopted a seven-day week, originally an astrological cycle naming each day after a classical planet and its associated god.

Hellenistic and Roman era

As Christianity spread, this astrological week merged with the Christian seven-day week centered on Sunday. In the fourth century AD, the first day was identified with the sun (Sol Invictus), a Mithraic god, and under Emperor Constantine this arrangement was Christianized. In AD 321, Constantine decreed a seven-day week in the Roman Empire, making Sunday a public holiday, a practice that spread across Europe and then the world.

The English names for the days derive from Germanic equivalents of the Roman names, except for Saturday, which retains the Roman Saturn. Which day is considered first varies by culture, though Saturday, Sunday, or Monday are the most common.

The three Abrahamic religions observe different holy days: Christians on Sunday, Muslims on Friday, and Jews on Saturday (Shabbat). The word "week" comes from a Common Germanic root meaning "turn, move, change." A week is defined as exactly seven days: 168 hours, 10,080 minutes, or 604,800 seconds. In the Gregorian calendar, a year has 52 weeks plus one day (or two in a leap year).