The term, loosely translated as "cooking place of the deer" or "cooking place of the wild," refers to a type of ancient outdoor cooking site found throughout Ireland and Britain, typically dating to the Bronze Age, roughly 2000 to 500 BC. They appear as low, horseshoe-shaped or kidney-shaped mounds of fire-cracked stone and charcoal-blackened earth, usually situated close to a water source. The one recorded at Levallinree in County Mayo is one such site, quietly occupying its place in the bog or field just as it has for perhaps three and a half thousand years.

The mechanics of a fulacht fia were straightforward but effective. A trough, usually timber-lined or cut into the ground, was filled with water. Stones were heated in a nearby fire and then dropped into the trough, bringing the water to a boil surprisingly quickly. Experiments have shown that a fulacht fia can boil water in around thirty minutes and cook a joint of meat in several hours. Once the stones cracked and splintered from the repeated heating and quenching, they were discarded to the side, gradually building up the characteristic mound that survives today. Ireland has somewhere in the region of four thousand to five thousand known examples, making them one of the most common monument types in the country, yet they remain poorly understood in terms of the full range of activities they supported. Some researchers have proposed uses beyond cooking, including brewing, textile processing, or bathing.