Introduction	Additional Stamp Impressions		A T Ms	Burelages	Cliche Cancellations	Cuts	Design Prints	Die-cuttings	Embossings	Form Prints
Gums	Hand Postmarks	Ink Jet Cancellations	Lumines- cences	Machine Postmarks	Margin Prints	Meter Stamps	Overprints	Pencancel- lations	Perforations	Press Marks
Print Substrates	Postal Stationeries	Punches	Reverse Prints	Roulettings	Second Overprints	Separate Productions	Se-tenants	Sheet Stamps	Silk Threads	Stamp Booklets
Stamped Envelope Overprints		Stamp Impressions	Third Overprints	Tress Rosettes	Watermarks	Others

Knowledge / Errors / Perforations

Perforation Error: philatelic term for a deviation caused by a perforation error

Missing Perforation: postage stamp caused by an error without perforation at all sides

Partly Missing Perforation: postage stamp caused by an error with missing perforation at one or more, but not at all four, sides

Pair With Missing Perforation in Between: pair caused by an error with missing perforation in between

Block of 4 With Missing Perforation in Between: sheet part caused by an error with missing perforation in between

Inverted Perforation: sheet caused by an error with 180 degrees rotated perforation

Double Perforation: postage stamp caused by an error with twice perforated at all sides

Partly Double Perforation: postage stamp caused by an error with twice perforated at one or more, but not at all four, sides

Perforation Size Error: postage stamp caused by an error with a different number of perforation elements at all four sides

Partly Perforation Size Error: postage stamp caused by an error with a different number of perforation elements at one or more, but not at all four, sides