The ratio of carbonated water to the syrup in a drink. If the ratio of carbonation to syrup is high then there is less flavor.
Rahm (to new guy): Is that what I asked for? If you waste my time, you waste the people's time.
New guy (aside to Rahm's assistant): It's just a Diet Coke.
Rahm's assistant: No way. The fizz ratio in McD's Diet Coke is perfect-soft on the bubbles. It's exactly the way Uncle Barry likes it.