An enclosure, in the broadest archaeological sense, is simply an area of ground defined by some combination of banks, ditches, walls, or palisades, and the term covers an enormous range of human activity across several millennia, from early medieval farmsteads to prehistoric ritual sites. What draws attention here is not dramatic visible remains but the quiet fact of designation without detail, a place that has been formally recognised as significant without that significance yet being fully explained.

The placename Killeen is itself suggestive. Derived from the Irish "cillín", it most commonly refers to a small unconsecrated burial ground, often used historically for unbaptised infants or others excluded from formal Christian burial. Whether the enclosure at this Killeen relates to any such use, or whether the name simply reflects an older ecclesiastical association now lost, is not established from available sources. Mayo's landscape carries layer upon layer of early settlement, and enclosures of various kinds, ringforts, cashels, monastic enclosures, field boundaries, appear throughout the county in considerable numbers, each with its own story at varying degrees of legibility.