The primary purpose of a calendar is to organize and keep track of time. It provides a structured way to divide the year into months, weeks, and days, facilitating scheduling of events, planning, and the observance of holidays and festivals. Calendars help coordinate daily activities, agricultural cycles, and social events in societies. They also play a crucial role in determining fiscal periods, academic years, and other significant timeframes for both individuals and organizations. Different cultures have developed various calendar systems, such as the Gregorian, Lunar, and Hebrew calendars, each with distinct features and historical significance.