Letters were forms of communication used before email, text messaging and BBM. Messages could be handwritten, typed with a typewriter, or printed from a computer onto paper. The paper, with the text and/or drawings on it, was called a letter.
The completed letter was inserted into an envelope and the physical address of the intended recipient was written on the outside of the envelope. A stamp was placed on the envelope to indicate that the sender had already paid for delivery service.
To learn what paper, typewriters, envelopes and stamps were, please consult a book on ancient history.
Senders then turned letters over to an organization called the “post office,” which was typically owned by the government. It was the post office’s job to deliver the letter to the recipient most of the time. However, to introduce elements of surprise and entertainment, the post office occasionally delivered letters to random recipients.
An air letter, also known as airmail, was one that travelled from the city closest to the sender to the city closest to the recipient (the actual recipient, not necessarily the intended recipient) by airplane instead of, say, train, truck, stagecoach or horseback.
There was also a second type of air letter. With this sort of air letter the sender could, if he or she knew origami, get a special piece of paper that would serve first as the letter and then, after complex folding, also as the envelope. The airmail postage was already paid on these special origami envelope/letter sheets.