Any "blob" or "extra metal" effect on a coin resulting from a sizable portion of the design on the die that struck the coin having fallen away or simply "moved" on the die itself (a.k.a. "retained cud"). A cud is distinguishable from a die break in that a die break is usually considered smaller and typically forms from a die crack.
List of known Cuds and Rim Cuds
Typical Minor Rim Cuds
Appears on any point around the rim and does not reach the field of the coin.
Typical Retained Cud Crack
Die Crack connecting at 2 different points
Typical Retained Cud W/Dispacement
Die state evolution
When found, cuds are often in and around the rims, earning the specific name "rim cud".
The most famous Morgan Dollar cud, which happens to be a rim cud, is found on the 1921-D VAM-1X:
In order for a variety to be listed for a rim cud, the cud must extend into the fields, not just into the denticles.
Please click this link for the full VAMworld.com definitions page.