A standing stone is a ritual or ceremonial monument of prehistoric date which comprises a single, or occasionally a pair, of upright orthostatic slabs, sometimes worked to shape, which may be surrounded by other smaller, stone settings, pits, burials and timber structures. The main upright stones vary in size from less than 1m to 6m high, and are recognised in the field as boulders, either upright or fallen, often quite conspicuous and close to other monuments such as stone circles and cairns. They are usually recognised by the main stone rather than any surrounding features. Some may also be revealed by place-name evidence and old maps. Where a group of three standing stones occurs this is a stone alignment.
Standing stones might be confused with cattle rubbing stones and still remain usually in the centre of fields, such as at Swingate, Cornwall, although it is possible that some cattle rubbing stones are actually reused standing stones. They might also be confused with Medieval boundary stones and early Christian monuments which were once painted. Low standing stones are often difficult to distinguish, especially on rocky expanses of moorland, and there is much scope for confusion with glacial eratics and small outcrop rocks, or the remains cairns, agricultural features and waymarkers. They may also be confused with heavily damaged stone alignments, long barrows or small stone circles.
Specifically excluded are Medieval boundary stones and mere stones and early Christian monuments.
Standing stones may have served as waymarkers, territorial markers, grave markers, cemetery markers, or meeting places. Suggested ritual functions have included their being objects of worship, phallic and otherwise. They may bare some relation to the movement of astronomical bodies. Associated features certainly indicate that they had some ritual function. They probably date from the Late Neolithic to the end of the Middle Bronze Age. They may overlap in function with other monuments of the same date.