In the early days, with fandom's focus on the prozines, this meant the top three prozines of the time. (See the discussion from Fancy 1 and Fancy 2, below.)
Later, the Big Three was more likely to refer to towering figures among pros during the Golden Age. Two were indisputable: Robert A. Heinlein and A. E. van Vogt who almost defined the new SF of 1938-1948. (The third of the Big Three was usually whoever among Asimov, Bradbury and Clarke the speaker liked best.)
|From Fancyclopedia 2 ca 1959
|The most important stfsy pros. Amazing Stories, Astounding Stories and Wonder Stories up to the early 40s; so called because for years they were the only prozines there were except for short-lived things like Flash Gordon, Miracle Science and Fantasy Stories, and Fanciful Tales. (Not counting Weird Tales, which wasn't science fiction.) From that time to about 1944 Astounding, FFM, and Unknown; after that till 1950, Astounding, FFM/FN, and the Standard Twins; thereafter and until the present Astounding, Galaxy and the Magazine of Fantasy and Science-Fiction.
|This is a fanspeak page. Please extend it by adding information about when and by whom it was coined, whether its still in use, etc.