A soda is a sparkling beverage.
In the North American sense, confusingly enough, it will be a beverage made from plain carbonated water, not “soda water.” Soda water has bicarbonate of soda (baking soda) in it, so it would affect the taste of the syrup being used to flavour the water with.
In the UK, however, “soda” in the beverage sense will indeed be presumed to be “soda water”, unflavoured, for use as a mixer in a drink, unless otherwise specified. At one time, countertop machines for home use were popular. They both fizzed the water for you, and flavoured it to make “pop.” Though they were popular purchases, most of them never actually got used, and now they are regular features at boot sales.
Sodaguns at bars can be set for only one carbonation level at a time, but they can have up to ten different product syrups attached to them. The problem is, different products can require different degrees of carbonation to be served correctly, as well as different ratios of syrup to carbonated water. It’s for this reason that bar dispensed soft drinks don’t always taste the same as those that come from cans or bottles.
French Sodas are made in the same way as Italian Sodas (see separate entry), but you top up the last 1/2 inch (1 cm) of the glass with milk or cream, stirring just enough so that it reaches half-way down the glass.
Generally, this style is not made with citrus syrups, as the citrus taste does not go well with the dairy taste.