Glaucus
Omono
Before Brexit the UK was part of the "Schengen" countries.
The Schengen area covers 26 countries ("Schengen States") without border controls between them.
See the map below for the current countries.
Schengen is not the same as the European Union. Norway and Switzerland were and are Schengen countries.
Ireland and the UK, as EU members, opted out of Schengen. UK was not part of Schengen, Ireland still is not.
Schengen refers to abolishing passport controls when people cross these borders.
Oh and sorry Iceland.