Chaff is dry, scale-like plant material such as the protective seed casings of cereal grains, the scale-like parts of flowers, or finely chopped straw. Chaff cannot be digested by humans, but it may be fed to livestock, ploughed into soil, or burned.

Threshing, or thrashing, is the process of loosening the edible part of grain from the straw to which it is attached. It is the step in grain preparation after reaping. Threshing does not remove the bran from the grain.