week

A week, in the Western and international context, is a unit of time equal to seven days. It is 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, or on average weeks in a month. The days of the week are often used to set work days, rest days, and holy days. The term "week" may also be used to refer to a sub-section of the week, such as the workweek and weekend. Certain weeks within a year may be designated for a particular purpose, such as Golden Week in China and Japan. More informally, certain groups may advocate awareness weeks, such as National Family Week in Canada, which are designed to draw attention to a certain subject or cause.

Some ancient and traditional cultures have or had different week lengths, including ten days in Egypt, an eight-day week for Etruscans and ancient Romans, and four- or five-day weeks between market days in modern West Africa. (See also the Japanese ten-day jun, used alongside the 7-day week.) The Romans later switched to a seven-day week. This was originally a so-called planetary or astrological week, a cycle of disputed origins which named each day after a classical planet and the god identified with that planet. Due to the spread of Christianity, the Romans' astrological week was identified and merged with the Christian seven-day week centred on Sunday (the day of the Resurrection of Christ), which had originated with the Jewish seven-day week centred on Saturday. Both the astrological week and the Jewish week may have been inspired by earlier seven-day cycles that existed in the Babylonian calendar, although the evidence for that is weak. In AD 321, Emperor Constantine the Great officially decreed a seven-day week in the Roman Empire, including making Sunday a public holiday. This later spread across Europe, then the rest of the world.