Wolfman Art - 3DS Max

Borders are open edges used strategically for welding. Generally use Border mode only if you are interested in closing open edges example: you have an object with open holes. Border mode allows you to select open edges then, switching to either vertices or edge mode, you can fill holes using bridge or weld.

Select edges switch to border mode go to edit borders and select "cap" -edges selected -switched to border mode and the "cap" option under edit border fills the gap. Super important when edges are all layered differently, or, this is how the software is reading it. Cap basically fills holes and is the most reliable option when improving the topology of your object.