The place-name itself offers a small clue. Greenan, or grianan in Irish, typically refers to a sunny place or a sunny chamber, and across Ireland the word is frequently attached to early medieval sites, sometimes hillforts, sometimes the residences of noble women, sometimes simply elevated spots that caught the light and the eye of those who named them. Whether the Greenan in Mayo carries any of that weight is, for now, an open question.

The enclosure belongs to a category of monument found widely across the Irish landscape. An enclosure in archaeological terms usually means a defined area bounded by an earthen bank, a fosse (that is, a ditch), a wall, or some combination of these, and such features can date from the Bronze Age through to the early medieval period and beyond. They served many purposes, from settlement and defence to ritual and agriculture, and without excavation or detailed survey it is rarely possible to say with confidence which function a given example served. This particular site in Greenan has been logged in the national record, which means surveyors considered it significant enough to document, but the detailed findings have not yet been made available in any accessible form.