A fizzy drink, a soft drink, a carbonated beverage.
I don't like the terms pop or soda. Pop sounds childish to me for some reason and soda makes me think of baking soda.
Usually I'd just say what the actual drink is (if it's Coke, then 'Coke', if it's Sprite, 'Sprite' and so on), also sometimes more general terms like 'lemonade' for more generic drink products.