Here is a cheat sheet for anyone starting out in stamp collecting or anyone interested in collecting stamps with printing mistakes.
Errors, freaks and oddities (EFOs) apply to any printing mishaps on stamps.
An error means the stamps turn out in such a way that they don’t have the appearance they were intended to have. This might mean it has the wrong colors, is missing something, has the wrong denominations, or another such mistake.
These days, errors are uncommon thanks to the careful watching of the printing process. However, the longest-run error on a stamp happened in 2011 on the U.S. Forever Statue of Liberty Stamp. The stamp showed the Statue of Liberty in Las Vegas instead of in New York. Somehow no one in the printing process noticed the error for three months.
Common kinds of errors include:
–Design error: Factually incorrect designs, such as a wrong inscription or a picture of the wrong subject.
–Value error: The wrong denomination printed on a stamp.
–Omission error: Something accidentally left out, like a color.
–Invert error: Like the infamous ‘Inverted Jenny’ stamp, a stamp printed upside-down.
–Double impression: A stamp printed twice, imperfectly overlapping.
-Imperforate error: Missing perforations on one or more sides.
A freak means a one-time mistake. Maybe a bug got into the system and ruined a single stamp, for instance.
An oddity is usable but has a slightly off printing mistake, like eyes on the top of a person’s head. Oddities are very common.
Some philately enthusiasts disagree on what exactly defines an ‘error’, ‘freak’, or ‘oddity’. The lines can be somewhat blurred on what each means. This article does a good job of explaining the debates over the labels of EFOs.