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

Knowledge / Errors / Perforations

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

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

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

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

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

Inverted Perforation: sheet with 180 degrees rotated perforation

Double Perforation: postage stamp twice perforated at all sides

Partly Double Perforation: postage stamp twice perforated at one or more, but not at all four, sides

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

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