A key part of the Brexit negotiations was about the border that separates Northern Ireland and the Republic of Ireland.
Last month, EU leaders approved a withdrawal deal with the UK that includes an agreement on the Irish border.
Both sides committed to avoiding the return of a “hard border” – physical checks or infrastructure – after Brexit.
This is where the controversial “backstop” comes in.
So what is the backstop?
The backstop is a position of last resort, to maintain an open border on the island of Ireland in the event that the UK leaves the EU without securing an all-encompassing deal.
At present, goods and services are traded between the two jurisdictions on the island of Ireland with few restrictions.
The UK and Ireland are currently part of the EU single market and customs union, so products do not need to be inspected for customs and standards.