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2.
The "period" of time wherein a woman's period, which normally happens monthly, happens only once in a year. This is usually the result of certain Period-controlling medications that can extend the time between periods to from between 3 months to 11 months.

The Yeariod will typically be a violent cataclysm of rage and decay, lasting a week and may be thought to contribute to global warming due to the heightened Btu output in yeariodites.
"Im on this new birth control pill and it makes my period come like only every twelve months, augh!

I feel like I'm about to get my yeariod!"
by Karlsefni February 03, 2011
 
1.
The yearly celebration of when a girl first started menstruating; a period anniversary.
My yeariod is January 5th.
by KoisoraRECYCLE April 10, 2009