Idem - Means that a later stamp issue has the same characteristics as a previous issue.
Illustrated Covers - A cachet which has words and an illustration.
Imperforate - An absence of perforations or rouletting between a pane’s individual stamps.
Impression - Any printing that is embossed or stamped.
Imprimatur - The first sheets of stamps produced from an approved plate.
Imprint Block - A block from part of a sheet where the printer's name or imprint appears on the margin.
Inclusions - Substances included while making paper used in stamp production.
India paper - A thin, tough opaque printing paper typically used for striking die proofs.
Indicium - The imprint made by a postage meter or found on postal stationery.
Inland mail stamps - Stamps intended specifically for domestic use.
Inscription - Any letters, words and numbers appearing in a stamp’s design.
Intaglio - Italian for "in recess.'' The stamp’s image is produced by the recessed portion of a printing plate.
Invert - Refers to any part of a design is inverted in relation to the remaining design.
Interleaves - Tissue used between stamp album pages to prevent stamp contact.