(Did you mean the fanzine?)
Originally called the costume party, the masquerade is a popular, event at most Worldcons and many other conventions. They are staged, formal, judged events, and there can be an elaborate protocol for participation, and they use a great deal of the tech budget for the con.
Experienced costumers spend many months crafting detailed costumes for these events, and often present short skits. Sometimes, although less commonly, fans pull together impromptu costumes at con. Early Windycons used to have a paper-bag masquerade, in which participants were given a paper bag full of random objects and required to construct costumes from the contents and whatever else they could find. An attempt to revive the custom in latter years failed, with a woman who'd brought her own Conanesque garb to the con angrily stomping on stage and announcing her presentation as "Barbarian with paper bag."
Costuming has been with us since The Beginning. Forry Ackerman and Morojo wore costumes at the first Worldcon, (NYCon I), and Dave Kyle wore another that won the first judged event at the second Worldcon, (Chicon I). Thus –- among a number of other things, of course –- Forry and Morojo pioneered hall costumes.
|From Fancyclopedia 1 ca 1944|
Part of the formula for a World Science-Fiction Convention. Some costumery had previously taken place among the Futurians, and Ackerman and Morojo went to New York dressed for Things to Come. The bal masque idea originated at a visit of Speer and Rothman to Fredk A. Kummer, Jr., and was adopted by the Chicon committee. It was suggested that convention attendees bring costumes representing characters from weird or science fiction, or from fandom; and the costume geared to suit the wearer's character. Accordingly, Skylark Smith came as C. L. Moore's Northwest Smith, Clarissa ditto as the nurse Mac which she had inspired in her pappy's Lensman stories, Speer as Buddy Deering, Kornbluth as the Invisible Man (gloves, bandaged face, goggles), Tucker as Hoy Ping Pong, Pogo as Hi Priestess of FooFoo, Widner as Giles Habibula, usw, and the prize-winner, Dave Kyle's Ming the Merciless by Leslie Perri. However, there were too few in costume, and next year, at the Denvention, a better story was told. E. E. Evans was first-placer for Bird Man of Rhea; Walt Daugherty had second with a spaceman's costuming involving airplane parts that would have cost whew if he hadn't picked them up as scrap. 4e 3d for the Hunchback of something, with a frickful mask. Morojo was a BEM, Widner Slan's Granny, Damon Knight John Star, Bill Deutsch Dr. Pinero of the Lifeline, Lowndes a zombie with a cut and bleeding throat, Israelite Chet Cohen the First Prophet of the Heinlein history of the future and numerous others.