Roto-annual 

An event occurring once every two years, or every other year. An alternative to the often confusing bi-annually, which means twice a year.

I was heading to the roto-annual Furcon in Baltimore, when all of the sudden the sandwich vendor ate a bird.

Roto-annual by Quhlena April 21, 2025

Rotoannual 

Every other year

Roto - Denoted from rotate.
Annual - Yearly

I was heading to the rotoannual Furcon in baltimore when all of a sudden I died

Rotoannual by Rotoannual Societ April 21, 2025