- 1: a system for fixing the beginning, length, and divisions of the civil year and arranging days and longer divisions of time (as weeks and months) in a definite order
- 2: a tabular register of days according to a system usually covering one year and referring the days of each month to the days of the week
- 3: an orderly list: as a : a list of cases to be tried in court b : a list of bills or other items reported out of committee for consideration by a legislative assembly c : a list or schedule of planned events or activities giving dates and details
- 4: British : a university catalog
The primary practical use of a calendar is to identify days: to be informed about and/or to agree on a future event and to record an event that has happened. Days may be significant for civil, religious or social reasons. For example, a calendar provides a way to determine which days are religious or civil holidays, which days mark the beginning and end of business accounting periods, and which days have legal significance, such as the day taxes are due or a contract expires. Also a calendar may, by identifying a day, provide other useful information about the day such as its season.
Calendars are also used to help people manage their personal schedules, time and activities, particularly when individuals have numerous work, school, and family commitments. People frequently use multiple systems, and may keep both a business and family calendar to help prevent them from overcommitting their time.
Calendars are also used as part of a complete timekeeping system: date and time of day together specify a moment in time. In the modern world, written calendars are no longer an essential part of such systems, as the advent of accurate clocks has made it possible to record time independently of astronomical events.