The term calendar is taken from calendae, the term for the first day of the month in the Roman calendar, related to the verb calare "to call out", referring to the "calling" of the new moon when it was first seen.
Latin calendarium meant "account book, register" (as accounts were settled and debts were collected on the calends of each month).
This is done by giving names to periods of time, typically days, weeks, months and years.
A date is the designation of a single, specific day within such a system.
A great number of Hellenic calendars developed in Classical Greece, and with the Hellenistic period also influenced calendars outside of the immediate sphere of Greek influence, giving rise to the various Hindu calendars as well as to the ancient Roman calendar.
Calendars in antiquity were lunisolar, depending on the introduction of intercalary months to align the solar and the lunar years.
In many old English legal documents dates in the months of January, February and early March give two years, for example, 1 January 1699/1700, and this has been the cause of much confusion.For the Scottish Old Parish Registers, however, a date of 1 January 1700 means precisely that.The English Julian calendar and the Scottish Gregorian calendar had not taken into account the actual length of the year leading to differences with dates in other countries in Europe.A calendar is also a physical record (often paper) of such a system.A calendar can also mean a list of planned events, such as a court calendar or a partly or fully chronological list of documents, such as a calendar of wills.The Julian calendar was no longer dependent on the observation of the new moon but simply followed an algorithm of introducing a leap day every four years.