Someone in my prom group sent out an email reminding the girls to get a garter. I’ve searched the web, but I still don’t quite get it. What is it? Do I have to get one? What do I do with it? So confused 
haha
From what I’ve deduced, you can wear a garter on your upper leg if you’re wearing a dress with a slit in it (or, if you want to lift up your dress to show it off for some reason, inside of any dress) to make you look “sexier…” I don’t really like them, but to each their own.
Presumably, it’s a garter you wear and save as a keepsake of the prom. Sometimes there are two and your date gets one, although you can see why a “tradition” like this isn’t appropriate for everyone. Personally, I don’t see why the prom ticket wouldn’t be more appropriate to put in the scrapbook.
ETA: Any ceremonies people might try to talk you into in which your date does the garter removal is even more inappropriate.