Ó Ceallacháin is an Irish surname that translates to "descendant of Ceallach," with Ceallach meaning "bright" or "warrior." This name is primarily associated with families from County Kerry and County Clare in Ireland. The Ó Ceallacháin family has historical ties to the Gaelic nobility and is part of the broader Irish clan system. The name is often anglicized as "Kelleher" or "Kelley," reflecting the variations in spelling and pronunciation over time.