The term refers to a type of prehistoric cooking or processing site found in great numbers across Ireland, typically identified by a horseshoe-shaped mound of fire-cracked stone surrounding a pit or trough. The standard interpretation is that water was heated by dropping stones made red-hot in an adjacent fire, which were then discarded in a spreading heap once they shattered from the thermal shock. That accumulation of burnt, blackened stone is usually how these sites are found.

The location itself is telling. The field southeast of Meenogahane pier is described as liable to flooding, and that detail is not incidental. Fulachtaí fia are almost always found near water, whether rivers, springs, or low ground with a reliable water table. Whether the proximity to water was primarily practical, ritual, or both remains a matter of debate among archaeologists, but the pattern is consistent enough that boggy or flood-prone ground has become one of the clearest indicators that a fulacht fia might be present. The site at Meenogahane fits that profile closely. It came to light through ploughing, which is how a significant number of Irish prehistoric sites have been identified, the soil disturbance exposing materials that had lain undisturbed beneath the surface.