A bullaun is a natural or worked boulder into which one or more cup-shaped depressions have been ground, typically by hand over a long period. The water that collects in these hollows was long considered to have curative or protective properties, and many bullauns remained in active devotional use well into recent centuries, accumulating layers of folk belief over whatever ecclesiastical or pre-Christian purpose first brought them into use.

Bullaun stones are frequently found in association with early church sites, holy wells, or the remains of monastic enclosures, though their exact function continues to be debated. Some researchers connect them to the grinding of pigments or grain; others regard them primarily as ritual objects. The truth is likely neither tidy nor singular. In Connacht particularly, bullauns appear in areas where early Christian communities established themselves in the early medieval period, often in low-lying or marginal land that the name element "callow" itself reflects, the word deriving from the Irish "caladh", meaning a riverside meadow or waterside pasture. That the stone at Callow has been recorded at all places it within a wider corpus of such monuments across Mayo, most of which survive without fanfare in fields, churchyards, or overgrown enclosures.

Beyond its location in the Callow townland of County Mayo, detailed information about this particular stone remains sparse at present, and little can be said with confidence about its precise condition, associations, or accessibility without further investigation on the ground.