Definition: A line which marks the limits of an area; a dividing line. (A limit of something abstract, especially a subject or sphere of activity.) [Oxford Dictionary] [边界；界线。多指作为界线的标识物等]

Example:

The fence marks the boundary between my land and hers. [这道栅栏是我的地和她的地的分界线]

Definition: 1. A line separating two countries, administrative divisions, or other areas. 2. The edge or boundary of something, or the part near it. [Oxford Dictionary] [较宽的边缘，边界，多指两国或两地之间的分界处附近的边缘地区、边界地带；也可以指物体的边缘等]

Example:

We crossed the Mexican borders into the USA. [我们穿过墨西哥边界进入美国境内]

Definition: A line or border separating two countries: 1. The extreme limit of settled land beyond which lies wilderness, especially in reference to the western US before Pacific settlement. 2. The extreme limit of understanding or achievement in a particular area. [Oxford Dictionary] [边界，边境，边疆，指靠近边界(boundary)的区域；也可引申为“未开发的领域”，“(学术的)前沿”等]

Example:

The American West was still a frontier a century ago. [一个世纪以前美国西部还是一片边疆]

Definition: The upper or outer edge of an object, typically something circular or approximately circular. [Oxford Dictionary] [边，边缘，尤指圆形或近似圆形的物体的边缘]

Example:

So the Pacific Rim has helped shape my view of the world. [因此，太平洋周边地区影响了我的世界观的形成]

Definition: 1. An edge or border. 2. An extreme limit beyond which something specified will happen. [Oxford Dictionary] [(道路、花坛等长着草的)边缘，引申为“某事即将发生之际”]

Example:

The grass verge outside the church.[教堂外面长满了草]

On the verge of war [战争爆发之际]