Gum Error: philatelic term for a deviation caused by a gum error
Gum Colour Error: deviation from the intended gum colour caused by an error
Design Print on Reverse: postage stamp caused by an error with design print on reverse instead on front
Missing Gum: postage stamp caused by an error without gum
Vertical Instead of Horizontal Ribbed Gum: postage stamp caused by an error with 90 degrees rotated ribbed gum
Horizontal Instead of Vertical Ribbed Gum: postage stamp caused by an error with 90 degrees rotated ribbed gum
Bark Gum: unregular thick and grazed gum caused by an error