what does the a in taser stand for
That’s the beauty of it - it doesn’t stand for anything.
From Wikipedia (they have cites):
“Taser is an acronym for a fictional weapon: Thomas A. Swift’s Electric Rifle.[11][12] Taser is a registered trademark. It has prompted a backformed verb to tase, which means “to use a Taser on”; however, to taser is also commonly used. However, as Taser is a registered trademark, lawyers may object to it being used as a verb.”
And according to this article, the Thomas A. Swift in question is the famous “Tom Swift” of science-fiction fame and “swifties” if you’re up on your wordplay.
http://www.inthesetimes.com/article/2894/
So technically the “A” stands for Tom Swift’s middle name but I don’t think the character actually had one. I guess the inventor of the Taser thought it sounded better with the vowel in there and it brings to mind “Laser”…