A souterrain is an underground passage or chamber, typically constructed from dry-laid stone and covered with large capstones, used in early medieval Ireland for storage, refuge, or both. They are often associated with ringforts, the circular enclosed farmsteads that were the dominant form of rural settlement in Ireland roughly between the fifth and twelfth centuries, and the pairing here at Ballyvelone fits that well-established pattern.

The ringfort itself, recorded separately, provides the context for what lies beneath it. Souterrains within ringforts were usually positioned close to the interior edge of the enclosing bank, sometimes accessible from a dwelling inside. The north-western placement noted at Ballyvelone is not unusual, though the precise form of the underground structure, whether a simple creep passage or a more elaborate series of chambers, is not documented in detail. What is known comes from local information rather than formal excavation, which means the site belongs to that considerable category of Irish monuments whose existence is accepted but whose full character remains unexamined.