(1) A Sound

from Fancyclopedia 2 ca. 1959
is the sound made by a ray-gun when it's fired, if you've not had occasion to notice. But a Zap-gun is a water-pistol, or sometimes a toy ray-gun. Martin Alger explains the ultimate source thus:

"At the Torcon they showed an atomic energy movie and a lot of the neofen were milling around during the showing. I asked Ben Singer if he were 'bored because nobody in the film has pulled a raygun and gone Zap! Zap!?'… I never heard the term used before this, so I guess that was the source."

Apparently, unbeknownst to any, a reporter was standing in the neighborhood, for the Toronto Morning Star headlines its convention report "Zap! Zap! Atomic Ray Passe with Fiends!" And, as Martin says, fans were delighted with this and the term caught on from there.
from Fancyclopedia 2 Supplement ca. 1960:
Shucks, Eney, Buck Rogers' rayguns were making this sound for many years before the Torcon. But they were not previously identified with the water pistols.

(2) An Australian Bookshop

Zap! is an SF bookshop in Brisbane, Queensland, Australia.

(3) An Apazine by Robert Briggs

An apazine for SAPS published by Robert Briggs.

Issue Date Pages Notes
October 1981

(4) A fanzine by Ted Johnstone

A fanzine published by Ted Johnstone

Issue Date Pages Notes
1 May 1957 14

This is a Stub APAzine page. Please extend it by adding information about when and by whom it was published, what APAs it appeared in, its impact on fandom, or by adding scans or links to scans.