The basic use of calendar is to identify the days so that we can inform, arrange event, keep record of the past that has happened. Days are important for religious, civil, or any other reasons. Calendar is an easy way to find out which days are holidays, religious etc. it also gives us useful information about the day.

It's a method where we name periods of date, days, and time. This is called as Dates Calendar. Rotations in calendar are usually contemporized with the perceived motion of astronomical objects. The most usage word to calendar is physical device. In different way we can see calendar in computerized system where we set reminder of future programs, appointments, planning, meetings, events, etc.

We can use calendar to connote a list of specific scheduled events. (For example: Court Calendar) . Usually a calendar includes day, date, month, and year. Islamic Calendar is an example where movement of Moon is contemporized to Lunar Calendar. As like Lunar Calendar a solar calendar is related on perceived seasonal variations arranged to the clear movement of the Sun; an example is the Persian calendar. Some other calendars are contemporized to movement of Venus.

In Lunar Calendar days are numbered within each lunar phase cycle. As the distance of the lunar month is not an even tiny proportion of the distance of the tropical year, a purely lunar calendar quickly wafts against the time of year. It is believed that Lunar Calendars are the oldest calendars to be invented by humankind.

Fiscal Calendar is where months are fixed to particular number of weeks to help linking from day to day, month to month, and year to year. The month of January have exactly five weeks. Month February has four weeks, Month March has four weeks etc. Usually this calendar has to add a 53 rd week after every 5 th or 6 th year, possibly added to month of December or may not be. The cycle of the days stars from Sunday and ends on Saturday.

Other calendar types: physical calendars, theoretical and mixed calendars, Complete and Incomplete Calendars, pragmatic etc.