A millennium (plural millennia or millenniums) is a period equal to
Sometimes, it is used specifically for periods of a thousand years that begin at the starting point (initial reference point) of the calendar in consideration (typically the year "1"), or in later years that are whole number multiples of a thousand years after it. The term can also refer to an interval of time beginning on any date. Frequently in the latter case (and sometimes also in the former) it may have religious or theological implications (see
There are two methods of counting years: current years (the count begins at the epoch) and elapsed years (the count is of completed years since the epoch). This latter method is used in India.
The original method of counting years was
The main issues arise from the content of the various year ranges. Similar issues affect the contents of centuries. Decades are usually referred to by their leading numbers and are therefore immune to this controversy: the decade called 1990s would by its naming not include 2000. Similarly the 100 years comprising the 1900s share 100 years in common with the twentieth century, but does not include 2000, and includes 1900.
Those following ordinal year names naturally choose
Those who are influenced by the leading digit equally naturally choose