>>97924582A leg garter. Originally used to hold up stockings before the use of garter belts or stockings that were tight on their own, but it's since been used as its own piece of lingerie. Also sometimes worn with a wedding dress as some kind of marriage tradition of symbolizing deflowering once the groom pulls it off her leg.
But mostly it's just something that's supposed to look sexy on a woman's thigh. So it was common to see it in cartoons on flapper girls or just to spice up a female character when she held up her dress for whatever reason.
