Definition: A cud is a damaged area resembling a blob on the surface of a coin which is raised above the field a little, and which obliterates the device or inscription where it appears. Cuds are the result of die cracks which have become severe, or from die chips where part of the die surface has become damaged and broken away.
Some experts in the error-variety hobby insist that for the blob to be called a cud, the damaged part of the die must include part of the edge of the die. Although this is the purist definition, in common parlance you'll see the term "cud" used to describe the blob created by any die chip or serious die crack, regardless of its placement on the die or coin.
Very small cuds are not usually valuable unless they appear on Proof coins. Cuds which can be seen by the naked eye are usually worth a small premium over normal value, and some cuds have actually been cataloged and are collectible, such as those on Morgan Dollars or between the letters of LIBERTY on Wheat Cents.
Re the double die it is very interesting but may need to be more evident to increase value, just a guess, good eye.
