Born/raised in Buffalo. Pop was any carbonated, flavored beverage. Coke was Coke. Soda was soda water. But "a" soda was ice cream with soda water and some flavoring (not to be confused with a float, which was ice cream, usually vanilla, and your choice of pop, i.e., a Coke float or root beer float). Milkshake was ice cream, milk, and maybe flavoring.
Here in MA, soda is any carbonated, flavored bev. What is a milkshake nearly everywhere else is a frappe here.
It's like when Ron said he was bringing spinach pies to the party. We know 'em as calzones (they were yummie no matter whatcha called 'em!).
It's all in where ya live!
Chuck