Cekoviu wrote:Soda and pop aren't really slang, just regional lexical items.
Pop is slang, but soda is not, because "soda" comes from the sodium compound that carbonates the water (ie: Club Soda).
The origin of "pop" varies depending on the source -- some say it comes from the "pop" sound of removing a cork from a bottle of soda (back when soda came in glass bottles with corks on them, I assume), though there seems to be an account of "pop" originating from a 19th Century beverage called "ginger pop", which does not appear to contain any sodium carbonation compounds, so your mileage may vary on that.
TL;DR - "Pop" is slang, "Soda" is not, and "soda" is the proper term for carbonated beverages.