There are three types that are viewed as 'errors' actually four if you consider damaged coins as errors, as most of the new collectors lump them into. 1. Die varieties are created on the die. So they are not a normal die. 2. Mint errors are most often a single coin event. 3. Die events started out as normal, but because of die aging, other distractions are caused on the die. 4. Damaged coins are just face value because they are not a mint error, just like a wrecked car is not a factory error.