Weeks are often organized as part of a larger calendar system. For example, in the Gregorian calendar, which is the most widely used calendar system today, the weeks are numbered sequentially throughout the year. Each week begins on a Monday and ends on a Sunday.
Weeks are used to measure the passage of time, especially for recurring events or schedules. For example, many people have a work schedule that is organized around a five-day workweek, with weekends off.
Weeks can also be used to measure longer periods of time. For example, months are often divided into weeks, and years can be expressed in terms of the number of weeks they contain.