It is biennial.
Biennial -sg that happens every alternate year.
Biennial means "occurring every two years," OR "lasting for two years." The word biannual can also mean "occurring every two years," although its most common meaning is "occurring twice a year."
Annal
The adjective is quadrennial. (extension of 1-annual, 2-biennial, 3-triennial) (The archaic word for a five-year period is a lustrum.)
Year 1000 was a medieval word. It was approximately in the middle of the Middle Ages. It starts with the letter Y.
It is biennial.
biennial
bi-ennial
Biennial -sg that happens every alternate year.
annual or anniversary
You could refer to it as a quarterly event.
Biennial means "occurring every two years," OR "lasting for two years." The word biannual can also mean "occurring every two years," although its most common meaning is "occurring twice a year."
An event occurring every two years is referred to as a biennial event. This pattern indicates that the event happens once every two years.
Bi, means 'every other'. For example: Bi-weekly, Bi-monthly, Bi-Anually
Biannual. Biannual can mean occurring every two years, OR occurring twice a year. Biennial, on the other hand, means only the former: occurring every two years.
Bi-annual = twice a year Bi-ennial = every two years
"bi" is prefix meaning every other, but it can be any time period. For example: Biweekly = every other week bimonthly = every other month Biennially = every other year