"Scots-Irish" is the term for the Scots who were planted in the
Northern part of Ireland. They were given the lands of the native
Irish, The English Crown said that the native Irish had forfeitted
their rights by the leaving of their kings (known as the flight
of the earls) in the 16th Century.
They emigrated to the states in large numbers and I think 5 American
presidents were Scots Irish of one or two generations.
Their concentration (55%-60%) in the North-East of Ireland is the
reason that Northern-Ireland is still part of the United Kingdom.