A burnt spread is essentially a deposit of fire-cracked stones and charcoal-rich soil, the residue of repeated burning activity, most likely associated with cooking or industrial processes during prehistoric times. They are often found near water sources and are closely related to fulachtaí fia, those low, horseshoe-shaped mounds of heat-shattered stone that litter Irish fields in the thousands, though a burnt spread tends to lack the distinctive mound form and may represent a different phase or pattern of use.

These features are generally dated to the Bronze Age, roughly 2000 to 500 BC, though some examples fall outside that range. The working theory for many such sites involves heating stones in a fire, dropping them into a water-filled trough to bring the water to a boil, and repeating the process until the stones crack and become useless, at which point they are discarded into a spreading heap. Whether this was primarily for cooking meat, producing steam in some kind of sweat-house arrangement, or serving industrial purposes such as working leather or textiles, remains a matter of ongoing discussion among archaeologists. The Glanlarehan example is recorded as a monument in its own right, which suggests it presents a distinct enough concentration of burnt material to be formally identified in the landscape, even if its surface expression is subtle.