The Irish Sea border is an informal term for the trade border between Northern Ireland and Great Britain. It was specified by the Ireland/Northern Ireland Protocol of the Brexit withdrawal agreement (February 2020), was refined by the Joint Committee in December 2020, and came into effect on 1 January 2021 following the end of the Brexit transition period. As a result of the Agreement, Northern Ireland remains aligned to the European Single Market in a limited way for goods, whilst remaining part of the United Kingdom customs territory and the UK internal market. Its effect is that the need for customs checks on the Irish border has been avoided, and a hard border has not been re-established.