Roughage is the part of some vegetables, fruits, and grains that your body does not really break down. It passes through you and helps your bowels move, so going to the toilet is easier. On food labels the usual word now is fibre (fiber in American spelling) — same idea, more official. Roughage is the older, homely word, the kind a parent or a school nurse might use: “Eat more roughage.” It is not a lab word, and it is a little vague. Though actually, people sometimes think it means food that feels rough in the mouth. That is not it. Soft banana has fibre too. Roughage is about what happens inside you, not about whether the food scratches your tongue.