Inside the US the situation is pretty clearly understood.
in reply to I refer to a non-specified carbonated beverage as a:
Outside the US (I have lived in many parts of Europe, the UK, Canada and Australia as well as the US)
this possibly applies:
Soda: Soda Water similar to club soda.
Tonic: Tonic Water - as in Gin and Tonic.
Pop: rarely heard
Soft Drink: Pretty universal where English is spoken
Fizzy Drink: Never heard it anywhere!
Pop: common in parts of Eastern Canada - used interchangeably with soft-drink.
jdtoronto - gee, guess where I live now :)