A skirt and too many ruffles if we're going with the kind most people refer too.

But just the skirt alone is stupid. You get more easily chilled and it can ride up too easily if it's caught on something. Not to mention things are more liable to scratch your legs because it's less protection. If you want to be decent, you have to worry about it all the time if you're doing any work that isn't a bunch of sitting. It's one thing to wear it to look pretty, but it's just sexism to make it a required uniform.

Petticoats is...some...underskirt thing.