International reply coupon
An international reply coupon (IRC) is a coupon that can be exchanged for one or more postage stamps representing the minimum postage for an unregistered priority airmail letter of up to twenty grams sent to another Universal Postal Union (UPU) member country. IRCs are accepted by all UPU member countries.
A British 1 Shilling IRC issued in 1959.
A 2021 Abidjan IRC, Mainland China's version (printed by Beijing Stamp Factory)
A postcard or post card is a piece of thick paper or thin cardboard, typically rectangular, intended for writing and mailing without an envelope. Non-rectangular shapes may also be used but are rare.
Example of a court card, postmarked 1899, showing Robert Burns and his cottage and monument in Ayr
Postcard depicting people boarding a train at the Shawnee Depot in Colorado, late 1800s.
Lipman's Postal Card
"Feldpost-Correspondenzkarte" (lit. field post correspondence card) used during the Franco-Prussian War of 1870