The border between two countries or regions is the dividing line between them. Sometimes the border also refers to the land close to this line.

A country that borders another country, a sea, or a river is next to it.

A border is a strip or band around the edge of something.

In a garden, a border is a long strip of ground along the edge planted with flowers.

If something is bordered by another thing, the other thing forms a line along the edge of it.