A bullaun is a large stone, usually boulder-sized, into which one or more rounded depressions have been ground or worn, typically by human hand. They are found across Ireland, often near early medieval ecclesiastical sites, and their purposes remain a matter of some debate among archaeologists. Ritual use, water collection, and the grinding of grain or pigments have all been proposed at various times, and many examples retain a folk association with cursing, healing, or the turning of water left standing in the hollow.

The Kilcolgan stone sits within a part of south Galway that has a long record of early Christian activity, and bullaun stones in this region are often linked to the remains of old church enclosures or to sites associated with local saints. The depression in such a stone was sometimes believed to hold water with curative properties, and communities maintained these associations well into the modern period, which is part of why so many bullauns have survived at all. They were not merely geological curiosities but objects with ongoing meaning for the people living around them, which gave them a kind of informal protection long before any formal designation existed.