A radiogram is a formal written message transmitted by radio. Often referred to as a radio telegram, radio telegraphic message - or just a telegram (although a telegram could be sent by landlines such as a telegraph line), these messages follow a standardized format and are sent using standardized transmission procedures. Various header sections exist in the telegram so as to minimize time needed to transmit the message over congested channels and to ensure certain blocks of information are included. Historically these have been used by government, military and amateur radio organizations. Generally email messaging has superseded radiograms but it too adheres to a standard RFC-5322 etc. Commercial radiogram formats were established at the International Radiotelegraph Conference (Madrid, 1932). Maritime radio service telegrams formats are set out in Rec. ITU-R M.1171, § 28. NATO has a standardized radiogram format which is also used by the American MARS system (example) and the Canadian Forces Affiliate Radio System (of which the Yellowknife Amateur Radio is a member).
Radiograms provide a written record of radio communications and an audit trail. When used in emergency situations, they provide evidence of what was happening and when. Maritime distress messages are public records regardless of who transmitted them. They are logged and the log can also be used to reconstruct what happened or what is happening as an emergency progresses. Obviously the application to emergency radio communications has an analogue in applying to emergency amateur radio communications in support of emergency measures (or Civil Defence).
In some contests, the sending of a message can be used to accumulate points. While a contest may be a leisure event, there is no mistaking that in the amateur radio service all contests have a serious exercise aspect to them.
A typical Radio Amateurs of Canada Radiogram can be found at: https://www.rac.ca/wp-content/uploads/files/ares//Radiogram-VA3IDJ-colour.pdf . The instructions on the bottom of the radiogram are self explanatory. This radiogram format is the same as the ARRL radiogram: https://www.arrl.org/files/media/Group/Fillable%20Radiogram%20Form.pdf . The Incident Command System (ICS) radiogram format is ICS 213, an example of which is at https://training.fema.gov/emiweb/is/icsresource/assets/ics%20forms/ics%20form%20213,%20general%20message%20(v3).pdf with instructions.
The British Columbia Provincial Emergency Radio Communications Centre (BC PERCS) has quite a bit of useful information regarding message handling including the following:
The Forms on that site include a PERCS Radiogram but also other forms including a Radio Log, Outgoing Message Register, Quick Message Form and Initial Impact Assessment Form. In Civil Defence matters the amateur radiogram is not in isolation but rather part of the operation of an Emergency Communications Centre (ECC).
Additional sources: