a sheet of lightweight paper, bearing an official postal stamp imprint, that is folded to form its own envelope and can be sent via airmail at a special, low rate because of its standard size, light weight, and lack of enclosures.
Introduction of the aerogramme – Australia Post
Aerogram – Wikipedia
Air Mail Ready to Write Aerogramme 1960
Australian Aerogramme ASC A34 10c 50th Anniversary of Qantas FDI