A mint error coin would be something with a wrong planchet, partial/missing cladding, broadstruck, partial collar, struck through error, struck through a capped die, an escaped capped die, and thousand other things. But keep in mind that a mint error is a one time striking event.
Some call die events errors. Such as die cracks, die breaks, internal die breaks, die chips, extreme die wear, split plating, extreme die polishing, extreme die abrasion, and on and on. These are die events. The die was normal when it was new. Now that it is aged, it is showing die events that happened to the die during its life. I call these die events. The difference between a mint error and a die event is this. A die event happens when the die is aging. 50% of the coins could show this on just one die. But a mint error is usually a one time event. Some die events are collectable. When the
Die Cuds start to show as these are often a end of the dies life. But common stuff to me is spendable change. New ones will save them, then when they are seasoned a few years, they realize the are common and then question, why they saved them.