The image to the left is an example of a 1989
Lincoln Cent that has a major die break, often
referred to as a "Cud".
"Cuds" are a type of die break. When an
area of the die breaks off, a gap in the die's
face is created. The coins struck by these
dies display a raised blank section. The
portion of the reverse of the coin opposite the
cud will be struck weakly due to the lack of
counter-pressure. A die break can only be
called a "cud" if the break occurs near the rim
of the die. Otherwise, they are just simply
referred to as a "die break".
Sometimes the die break will not fall off
completely, and the resultant strikes are
referred to as "retained cuds".
Images courtesy of Steven Bingham