A combination of "granny"/"grandma" and "panties".
1. Large underwear usually worn by old women/fat transvestites. Made of cotton (because it breathes) or a fat-holding-in material (like lycra or spandex), granties typically begin directly under the breasts and cover the entire ass (and sometimes thighs) and come in white, nude, or pastel floral prints.
2. The chastity belt of the modern age. Worn by a woman when there is no chance of them being seen by a potential sexual partner or to encourage abstinence.
3. Underwear that your mother buys you because, let's face it, her ass is down to her knees and she hasn't gotten laid in years so she really doesn't know any better.
See Also: granny panties.
-Shut up cuntbag, my mom bought them for me!
-Where'd she get those... the toilet store?
-No, Wal-Mart.(insert sad face)
-I'm never going to get laid. (insert sad face)
-You're not going out, are you?
-Yes mom, I have a date.
-Oh my, what underwear are you wearing?
-Oh no you're not! Go change into some granties first!
-Oh mom, do I have to?
-Yes, you filthy whore. I don't want some illegitimate grandchildren to raise because you can't keep your legs shut.
-Hey, if my mom had made me change my underwear when I was your age we wouldn't be having this discussion... because you wouldn't have been born and I would have graduated high school. Now get in there and change before I whip your ass!
I made this term up when I was acting as a grandmother to my great nephew...it's a special status as an "aunt". Kids have aunts and great aunts, so this gives the great aunts a special name.