Errors-Freaks & Misprint Stamps
As a general rule of thumb, if something is not as it should be, then it is an error, freak or oddity. EFO's are the result of an accident of some kind during the production process. It is a unusual aspect of stamp collecting that an error may be worth considerably more than the perfectly normal stamp. EFO's are valuable because there are so few of them and they are regarded as collectable.
