One Definition of the "Scots-Irish" are as a People

Ulster-Scots are an ethnic group in Ireland, descended from mainly Lowland Scots who settled in the Province of Ulster in the north of Ireland. The term Ulster-Scot refers to both the Scottish Presbyterian settlers of the 17th century and, less commonly, to the gallowglass who arrived from what is now northwest Scotland centuries prior to the Scottish Reformation. Settlement of the former first began in large numbers with the Plantation of Ulster, a planned process of colonization which took place in the reign of James VI of Scotland and I of England.

Ulster-Scots were largely descended from immigrants from Galloway, Ayrshire, and the Scottish Borders Country, although some descend from people further north in the Scottish Lowlands and the Highlands. Ulster-Scots emigrated in significant numbers to the United States and all corners of the then-worldwide British Empire — Canada, Australia, New Zealand, South Africa — and to a lesser extent to Argentina and Chile in South America. Scotch-Irish is a traditional term for Ulster Scots who later emigrated to what is now the United States; "Scots-Irish" is a more recent form of the American term, and is not to be confused with Irish-Scots, i.e., recent Irish immigrants to Scotland.