Definitions of roughage on the Web:

• coarse, indigestible plant food low in nutrients; its bulk stimulates intestinal peristalsis
  wordnetweb.princeton.edu/perl/webwn

• Dietary fiber, sometimes called roughage, is the indigestible portion of plant foods that pushes food through the digestive system, absorbing water and easing defecation.
  en.wikipedia.org/wiki/Roughage

• dietary fibre
  en.wiktionary.org/wiki/roughage

• Feed that is high in fiber, low in digestible nutrients, and low in energy (eg, hay, straw, silage, and pasture).
  www.epa.gov/oecaagct/ag101/beefglossary.html

• food that is high in fibre such as hay, corn and straw
  www.soilassociation.org/web/sa/saweb.nsf/a71fa2b6e2b6d3e980256a6c004542b4/3f488deea330775f80257149004fc2c8!OpenDocument

• feed high in fibre (greater than 18% crude fibre); tends to be bulky, coarse and low in energy. See Forage.
  www.omafra.gov.on.ca/english/livestock/dairy/facts/08-039.htm

• A misleading term that is often used to describe the Fibre content of a diet. This is misleading farmers to believe that the fibre portion of the ration’s only purpose is to aid digestion, without reference to the digestibility of that fibre source. ...
  www.blue-mountain.net/feed/terminology.htm

• A low-quality forage such as hay that was too mature when cut, or crop residues such as wheat straw or corn stalks.
  animalscience.ag.utk.edu/ITCModules/glossary.htm