From the 1 January 2021, the UK and EU have agreed that checks will not take place at the border between Northern Ireland and the Republic of Ireland.
When trading goods, companies in Northern Ireland will continue to follow many of the EU's rules, meaning that lorries can continue to drive across the border without having to be inspected.
However, there will be a new "regulatory" border between Northern Ireland and Great Britain (England, Scotland and Wales). That's because, unlike Northern Ireland, Great Britain won't have to follow EU rules in the future.
Further information on the Northern Ireland Protocol can be found here.