A calendar is a system of arranging days and longer divisions of time such as weeks and months in a sequential or definite order. According to the Gregorian, a calendar year is a twelve month period starting from 1st January to 31st December. It has a maximum of 365 days on a common year while the leap year has a total of 366 days. Creating a calendar involves giving names to periods of time e.g. days, weeks, months and years. There are other definitions of a calendar that gives a different meaning depending on the explanation.
It can also mean a list of planned events such as a full chronological list of documents i.e. a calendar of wills. In most situations, the months and years highlighted by a calendar are synchronized with the rotation of the sun and moon. The lunisolar calendar is the most popular type of a pre-modern calendar. Unlike the other types of calendars, on intercalary month is added occasionally to remain synchronized with the solar year over the long term. The common calendar has indications of dates that mark special events such as a holiday, or weekends. They are highlighted with a different color and may vary depending on the number of holidays in a given country.
They not only give the full outline of the months in a year but also show the current date and time. The Gregorian calendar, introduced in 1582 is the first calendar reform of the early modern era. It is based on observation of a long-term shift between the solar year and the Julian calendar.
A full calendar system is made up of a different calendar date for each day. This means that the week cycle is not a full calendar system by itself. Naming the days within a year without a system that identifies the years does not fall into the category of a full calendar system. A straightforward calendar system will only count time periods from a reference date and it is applicable in the Unix Time or Julian day.
However, the computations in these systems are only a matter of addition and subtraction. There are calendars which have multiple larger units of time. A solar calendar assigns a particular date to each solar day while lunar calendars have its days numbered within each lunar phase cycle. The lunisolar calendar is one that compensates by adding an extra month to the cycle to realign the months with the seasons.