An air letter of very lightweight paper: Sandy wanted to send her mother an aerogram which she found out was only one piece of thin paper to be folded forming its own envelope and which could be sent at a low postage rate.

1. A roentgenogram of a part of the body after it has been injected with air: The term aerogram is sometimes used in medicine for the word "pneumogram" or for "bronchogram".
2. A letter designed for airmail consisting of a single sheet of lightweight paper that, once written on, can be folded and sealed to form an envelope; air letter: Jenny used to use aerograms to send letters to her mother, but now she uses emails instead!

The dated term aerogram can also be described as a wireless message.

At one time, it was a telegram and part of its journey was accomplished by an aeroplane (airplane).
3. A message sent "through the air": It used to be that an aerogram was sent by the way of radio!