Tagging : The marking of stamps with a phosphor or similar coating (which may be in lines, bars, letters, overall design area or entire stamp surface), done by many countries for use with automatic mail-handling equipment.

Telegraph stamps : Stamps used for the payment for the use of a telegraph service.

Testing label : A stamp sized label used for testing automatic stamp vending machines.

Tete-beche : Two adjoining stamps with one being upside down in relation to the other.

Thematic : A stamp collection that relates to a specific theme and is arranged to present a logical story and progression. Some of the collecting themes are Aircraft, Architecture, Animals, Army, Astronomy, Birds, Bridges, Buildings, Butterflies, Cars, Cats, Chess, Cricket, Disney, Dogs, Explorers, Fish, Football, Heraldry, Horses, Famous People, Flowers, Fauna, Gardens, Golf, Insects, Lighthouses, Medical, Royalty, Rugby, Shells, Ships, Space, Sport, Technology, Trains, Writers.

Tongs : A tweezers-like tool with rounded or flattened tips used to handle stamps.

Topical : Indicates a group of stamps with the same theme—space travel, for example.

Tied : A term used when a stamp is cancelled with a postmark which straddles both the stamp and cover.

Tone spot : A mark on a stamp of brown rusty appearance which detracts its value.