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 &ndash although not strictly part of – the calendar. In many languages, the days of the week are named after classical planets or gods of a pantheon. In English, the names are Sunday, Monday, Tuesday, Wednesday, Thursday, Friday and Saturday, then returning to Sunday. Such a week may be called a planetary week. This arrangement is similar to a week in the Bible in which the seven days are simply numbered with the first day being a Christian day of worship (aligned with Sunday) and the seventh day being a sabbath day (Saturday).