A die break is deeper than a die crack is actually a wider die crack, can result in a part of the die falling out and when it is rim to rim it is called a CUD. A CUD can be retained as in the image below or that part of the die can fall out and fill in with planchet metal forming what looks like a was of CUD; see first image.
A Cud is a die break that connects rim to rim and is only called a cud because it looks like a wad of cud in shape. So there’s no such thing as a cud mint error, it’s just a name applied to this particular type of die break.
Most of the dies breaks form a half circle as the break only occurs on the rim or edge of the die’s design. When this piece breaks out then the planchet metal is squeezed into this cavity, forming the cud shape.
If however the die break does not break out then it’s referred to as a retained cud or die break and you will see the die crack starting at one point of the rim then “circling” back to another part of the rim. Unusually these die breaks are deep and the crack looks thick and jagged when in the retained state.