roughage

Short definition from Wiktionary

Noun

1. 1
   Originally (archaic), garbage, rubbish, or waste; later (agriculture) the portions of a crop which are discarded, such as husks, stalks, etc.; also, agricultural waste such as weeds.
2. 2
   Coarse or rough plant material such as hay and silage used as animal fodder.
3. 3
   Substances, generally of plant origin, consisting mostly of complex carbohydrates which are undigested when eaten by humans, and which therefore help the passage of food and waste through the alimentary tract; dietary fibre.