Disruptive coloration
This term is used to describe the way in which a butterfly or moth's appearance is visually broken up, usually by means of mottling and / or prominent lines.
The Angle Shades moth Phlogophora meticulosa is a good example - it is equally well concealed when settled amongst dead vegetation or fallen branches.
Predators - particularly birds, use a "search image" to locate resting moths. They look out for a "moth shaped" object, but the disruptive pattern of the Angle Shades breaks up it's outline and foils the bird's search image.