In Irish the term bullán means a 'bowl or a round hollow in a stone' (Dineen 1927). The anglicised term 'bullaun' has been adopted to refer to artificial basins or hollows in rocks, boulders or small stones. The stones are usually unworked, except for the basin, and they vary in size from small and easily portable to large, earthfast boulders. The hollows are usually circular and the profiles vary from very gently sloping to vertical and flat-bottomed. Though most bullaun stones contain only a single basin, double and multiple bullauns are also known. Examples of the latter type can be seen at Grove and Kilmakeldar. Circular hollows are also a feature of Bronze Age rock art but these are usually distinguished by their smaller size and by their association with other motifs.
Several suggestions have been put forward as to the purpose of bullaun stones. The majority of the known examples are found on sites with early ecclesiastical associations and they are commonly referred to as fonts. By the 11th and 12th centuries AD, legends had already become attached to some stones (Price 1959, 161-88). and in local folklore some are explained as Saints' knee-prints or pillows, and water in some is thought to have curative powers. The Keelers/Na Beistí, at Kilmakeldar, is associated with the legendary Glas Ghaibhneach, a miraculous cow who provided an unfailing supply of milk. Cloghnagalt is traditionally the repository for milk and food provided for the mad people who came to Gleann na nGealt to be cured. However, it is likely that the original purpose of bullauns was of a more practical nature, as mortars for crushing and grinding various foodstuffs such as herbs, roots and cereals (Price 1959; Hughes and Hamlin 1977, 99-100). Similar stone basins were used until recently for pounding barley, furze and other foodstuffs. Bullaun stones may also have been used for grinding metal ores.

from Corca Dhuibhne - Dingle Peninsula Archaeological Survey Oidreacht Chorca Dhuibhne, 1986