field postcard
/ˈfiːld ˌpəʊs(t)kɑːd/Now historical
noun
A postcard designed for use by soldiers in the field; a postcard of a type sent by a soldier in the field.
Origin
Late 19th century; earliest use found in Stamp-collector's Magazine. Originally from field post + card, after German Feldpostkarte; subsequently reinterpreted as from field + postcard.