A week is a period of seven successive days that is usually understood to begin with Sunday and end with Saturday, states Reference.com. A week is a unit of time that is artificially devised with no basis on astronomy.
The origin of the term "week" is usually associated with the ancient Jews and the biblical account of the Creation, which states that God labored for six days and rested on the seventh. According to the Encyclopedia Britannica, there is evidence indicating the ancient Jews may have borrowed the idea of the week from Mesopotamia. This evidence is based on the fact that the Sumerians and the Babylonians divided the year into weeks of seven days each. Additionally, one day in each of the Sumerian and Babylonians weeks was designated as a day of recreation.