The odd one out is A. Calendar.
A calendar is a system of organizing days for social, religious, commercial, or administrative purposes. A calendar is also a physical record of such a system. A calendar can also mean a list of planned events, such as a party calendar or a sports calendar.
A year is a period of 365 or 366 days, as measured in the Gregorian calendar or in any calendar based on a year of 365 days, such as the Julian calendar. A year is also the time it takes for the Earth to orbit the Sun once.
A date is a specific day or date on the calendar. A date can also mean a particular point in time, such as the date of a meeting or the date of a birth.
A month is a period of 28, 29, 30, or 31 days, as measured in the Gregorian calendar or in any calendar based on a month of 28, 29, 30, or 31 days. A month is also the time it takes for the Moon to orbit the Earth once.
A day is a period of 24 hours, as measured in the Gregorian calendar or in any calendar based on a day of 24 hours. A day is also the time it takes for the Earth to rotate once on its axis.
In the given options, all are related to time except calendar. A calendar is a system of organizing days, but it is not a day itself.