You have to name all the countries in the world which have an open border.
An open border is a border that enables free movement of people (and often of goods) between jurisdictions with few or no restrictions on movement, that is lacking substantive border control.
Treaties for making border open is provided as a hint.
Really, I copied them from a popular website. I will check whether that website also had wrong spelling. BTW Thanks for noticing and it is correct now.