- 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.
the mixture of fecal material and plant matter left by an animal, esp. an insect, after it has eaten its way into a tree, plant, etc.
Debris or excrement produced by insects.
Origin of frassGerman, 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.