letter card

noun British.

1. a large postal card, with gummed edges, that can be folded lengthwise and sealed with the message inside.

noun

1. a card, usually one on which the postage is prepaid, that is sealed by being folded in half so that its gummed edges come into contact with each other
2. a long card consisting of a number of postcard views, with space for writing a letter on the backs, that is folded like a concertina for posting