• The boundary of an area of land is an imaginary line that separates it from other areas.
  • The Mississippi River [密西西比河] forms a natural boundary between Iowa [爱荷华州] and Illinois [伊利诺伊州].
  • The stream curves round to mark the boundary of his property.
  • We walked through the churchyard towards the boundary wall.
• The boundaries of something such as a subject or activity are the limits that people think that it has.
  • the boundaries between work and play
  • within the boundaries of the law
  • the boundaries of human knowledge
  • new scientific discoveries that are stretching the borders of knowledge [区分也没有那么严格啦]

• 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.
  • The river lies on the border between the US and Mexico.  

• A border is a strip or band around the edge of something.
  • writing paper with a black border
• In a garden, a border is a long strip of ground along the edge planted with flowers.
  • a flower and shrub [灌木] border
• A country that borders another country, a sea, or a river is next to it.
  • countries that border the Mediterranean [地中海]
• If something is bordered by another thing, the other thing forms a line along the edge of it.
  • His confidence bordered on arrogance [傲慢].

抄自柯林斯+LDOCE.