Postage stamp errors refer to mistakes made during the printing or design process that result in a stamp differing from the intended design. These errors are often rare and can make certain stamps more valuable to collectors. Here are some common types of postage stamp errors:

1. Color Errors
Misprints or wrong colors occur when the ink or printing plate is incorrect, leading to stamps being produced in colors that differ from what was intended.
Example: A stamp designed with a red background might accidentally come out with a blue background.
2. Inverted or Reversed Images
Inverted stamps occur when the design, such as the image or text, is printed upside down. Sometimes, this happens with overprints or even the whole design.
Example: The famous Inverted Jenny from the U.S. (1918), where the airplane was printed upside down on a stamp, is a classic and valuable error.
3. Misperforations
Misperforations refer to mistakes in the perforation (the holes punched to separate individual stamps), leading to stamps that might have perforations in the wrong places or uneven spacing.
Example: A stamp might be printed with its perforations too close to the design or cut off entirely.
4. Watermark Errors
Some stamps have a watermark (a design or pattern visible when held up to light). Errors occur when the watermark is misapplied, leading to misaligned or absent watermarks.
5. Overprint Errors
Overprinting errors happen when additional printing (such as a denomination change, commemorative text, or special marking) is misaligned or applied incorrectly.
Example: A commemorative stamp might have the overprint for the year “2025” placed upside down or too far off-center.
6. Missing or Double Prints
Sometimes, a stamp might be produced without one or more key design elements (such as missing a value) or with the same design element printed twice.
Example: A stamp may have a missing country name or the text might appear in a double layer, giving it a blurry appearance.
7. Die Cut Errors
Die cut errors occur when a stamp’s shape is not correctly die-cut, making it come out irregular or misshaped. It may have extra corners or be cut in a strange shape.
8. Inverted Overprints
This error occurs when an overprint on the stamp, like a surcharge or additional text, is printed upside down or in the wrong orientation.
Collectors often seek out postage stamps with these types of errors for their rarity and uniqueness. Some errors, like the Inverted Jenny, can be worth tens of thousands or more, depending on the rarity of the mistake.