A week is a unit of time longer than a day and shorter than a month. In most cultures, the week is seven days long, though five-day and ten-day weeks have been used. Many cultures have set aside one day every week as a day of rest or a day of religious observances.
Days of the week
In the United States, the week conventionally begins on Sunday, followed by Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday. The names of the days are taken from the Norse gods. In much of Europe and Latin America, the week begins on Monday.
The religious observance of a day of rest or prayer is termed sabbath. The Jewish sabbath is on Saturday. Christians observe the day of rest on Sunday, though some sects (particularly the Seventh-Day Adventists) observe the sabbath on Saturday, in keeping with the Jewish rule. Muslims observe the sabbath on Friday. The word for Saturday is derived from "sabbath" in the Greek language and in the Romance languages.