A soda fountain or postmix machine is a device for dispensing carbonated soft drinks. They typically consist of a boxy device featuring multiple dispenser heads and a drip tray beneath them. They may feature an ice cube dispenser in the middle of the device. The machine makes carbonated soft drinks by combining flavored syrups, water, and carbon dioxide. They're common in fast food restaurants and concession stands.
The drinks dispensed by a soda fountain are called a "fountain drink."
They're named after small eating establishments that used to serve carbonated drinks by a "soda jerk," a person who mixed flavored syrups with carbonated water.