Short for "convention" – more specifically, a science fiction convention. Common terms used in science fiction – ftl, time-travel, warp, blaster and the like – are "conventions of science fiction"; gatherings of various fans and pros from distant points (usually held in a hotel, frequently for more than a single day and often discussing sf where they have programs) as a one-time or annual event are "science fiction conventions."
|From Fancyclopedia 2 ca 1959|
|Comingtogether of fans from various localities, usually at a call issued by some organization or local group. And the designation is used as a combining word to make up some distinctive name for the brawl -- either "con" itself or its completions, -vention, -ference, -clave, or -fabulation. These words are not equivalent, for convention usually refers to the principal annual gathering; other formal get-togethers are conferences or conclaves. A confabulation is an informal meeting larger than a mere fan visit but not built up or conducted like a conference; the word is pretty near obsolete, tho popular in the early 40s.
The most important thing about a con is that the slans can get together with their own kind of people, perhaps forgetting their introversion for a while, and do what they want to do and fangab about mutually interesting things and develop their stfnic personalities.