Shabbat
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Shabbat in Judaism is one day of the week (from when the Sun goes down on Friday until it gets dark on Saturday) when work is not allowed according to the Ten Commandments. It is a day of rest and of Torah study. Most machines may not be operated, and no work done. Not even a light switch can be used. Not all sects are strict about this. One who is strict is called an Orthodox Jew.
The Sabbath in Christianity is the same idea, but usually less strict, depending on the denomination. Sunday is the day of rest for most Christians. It is often on this day that Christians go to worship at a church.
Islam also has this concept.
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