Sorry, but what is a bustle?

How did they sit down or go to the bathroom? All of it seems very impractical

Most people on here say that bustles started after hoopskirts fell out of fashion. However bustles were used to lift up the back of hoopskirts as well, the bustles were just plain, smaller, and under the skirt instead of on display. example

I hope it's ok to ask this here but what is a hoop?