auntie flo 

A nickname/code word used as an alternative when a girl or woman is on her menstrual cycle or her period.

jane: "hey betty, you wanna come over after school today?"

betty: "nah, i'm having a visit from auntie flo and i don't feel too well about it."

auntie flo by H.J.S. July 28, 2006

auntie flo 

A colloquial expression for a woman's menstrual cycle.

Auntie flo can also be used in limericks, such as here:

There once was an auntie called flo.
She was sexy and red like Bordeaux.
When she met a vibrator,
She said: come back later,
Cuz today I prefer a regular Joe.

auntie flo by kinkylimerix January 11, 2015