A refrigerator (colloquially fridge) is a common household appliance used to keep food or other perishables cooled to a temperature below the ambient temperature of the room. It consists of a thermally insulated compartment and a heat pump (mechanical, electronic, or chemical). The refrigerator is a relatively new kitchen appliance, having replaced the icebox.
Refrigeration is the process of removing heat from an low temperature enclosed space to a higher temperature region.
Before mechanical refrigerators were introduced, people cooled their food with ice and snow. People dug holes in the ground and made cellars lined with wood or straw, then filled them with ice. This was how people refrigerated their food for most of history. When ice was unavailable, perishables would sometimes be placed underground anyway, to keep them slightly cooler. Dumbwaiters would sometimes be used to hold food underground, then easily bring it up to the kitchen when needed.
The first known artificial refrigeration was conducted by the Muslim physicist and chemist Ibn Sina. He explained away his achievement as some form of engineering relying only on natural processes.