A calendar week is the cycle of seven named days in a calendar. 

The names of the seven days have varied but the seven-day week itself has been continuously maintained from early times. It was reputedly started by the ancient Assyrians but subsequently, the various Roman and Christian calendars, the Islamic calendar and the Saka (Indian) calendar all use the seven-day calendar week. Egyptians used a 10-day week, as did the Chinese. The Mayans had two, a thirteen-day week and a twenty day week but the Roman and later the British empires made the seven-day week the universally popular one.