The original single A was for amazon: "FANG was an acronym coined by Jim Cramer, the television host of CNBC's Mad Money, in 2013 to refer to Facebook, Amazon, Netflix, and Google. Cramer called these companies "totally dominant in their markets" [0].

[0]: https://en.wikipedia.org/wiki/Big_Tech#FANG,_FAANG,_and_MAMA...