The dictionary definition of a border is: "a line separating two political or geographical areas, especially countries." Most countries in the world share their border with at-least one more country. China shares its borders with 16 other countries, Russia with 14. At the same time, Australia and Japan don't have any neighbors.
Borders can be peaceful and open (European Union), tense and closed (North/South Korea) or variation of both. Below, you'll see incredible examples of the starkly different, as well as the wonderfully similar borders around the world.

1. East and West Berlin, Germany