Aero-grammes, also known as air letters, are a type of lightweight letter that is sent by airmail. These letters were introduced in the early 20th century, and they were often used by people who needed to communicate with loved ones who lived far away. There are a few synonyms for the term "aero-grammes" that you may come across, including aerogram, air letter, and stamped aerogram. These terms are all used to describe the same thing, and they are all commonly used in different parts of the world. Regardless of which term you use, aero-grammes remain an important form of communication, particularly when sending letters across long distances.