Grannys or grannies are underwear worn by grandmothers. Which typically refer to overly large but practical briefs commonly worn by grandmothers & "femmes d'une certaine age." Also used as a tease or insult among young women.
The ladies were throwing their grannys onto the stage.
I hope you are not going to wear your grannies tonight.
I hope you don't go out and buy more grannys again.
Beneath those grannies there is wisdom.