Aerogramme

An aerogram, aérogramme, air letter or airletter is a thin lightweight piece of foldable and gummed paper for writing a letter for transit via airmail, in which the letter and envelope are one and the same. Most postal administrations forbid enclosures in these light letters, which are usually sent abroad at a preferential rate. Printed warnings existed to say that an enclosure would cause the mail to go at the higher letter rate.

The use of the term aerogramme was officially endorsed at the 1952 Universal Postal Union Postal Union Congress in Brussels. Thereafter, the term air letter quickly faded from use.

Most aerograms have an imprinted stamp indicating the prepayment of postage. As such, this meets the definition of being postal stationery. However, some countries such as New Zealand, Zimbabwe and Ireland, sell unstamped aerograms. Unstamped aerograms are referred to as formular aerograms and can be issued by either postal authorities or by private companies. Senders are required to write their name and address on the reverse.

The aerogram was largely popularized by its use during the Second World War (1939–45). Lieutenant Colonel R. E. Evans, Royal Engineers, Assistant Director Army Postal Service Middle East Force (MEF), proposed that a lightweight self-sealing letter card that weighed only 1/10 oz be adopted by the British Army for air mail purposes. He recommended its use to Sir Anthony Eden, the Secretary of State for War during his visit to the Middle East, in late 1940. By January the following year, General Archibald Wavell, 1st Earl Wavell, the Commander-in-Chief, MEF was told by Eden that "Your Assistant Director Army Postal Services may forthwith introduce an Air Mail Letter Card Service for the Middle East. Use British stamps from all countries, including Egypt.".

...
Wikipedia