Masks versus Borders - confused

[rad2689 Profile Private message]

Can someone tell me what the difference is between masks and borders. I am trying to determine the difference and having a hard time grasping it. I know that with a mask black hides everything underneath and white shows everything underneath and grey will show a varying amount of whats underneath depending in how light or dark the grey. My question is what is the difference with a border - does it not do the same thing? Sorry for the dumb question.