- The definition of frass is the waste left as an animal's bowel movement.
An example of frass is what a bug excretes after eating a leaf.
frass definition by Webster's New World
frass definition by American Heritage Dictionary
Origin: German, feed, result of eating, insect damage, from Middle High German vrâz, from Old High German frāz, from frezzan, to eat; see ed- in Indo-European roots.