It can mean a few things depending on who you ask.
1) You discuss contact and you and your Ex agree not to contact one another.
2) You disappear without letting the other person know what happened or where to find you.
3) You let them contact you but you put hardly any effort in replying and occasionally throw them a crumb to see if they reply or get the hint that there is a problem.
Clearly, option 3 is cowardly.
Option 2 is also weak.
Option 1 is the best. You both know where you stand.
It is ethical and the the best way to end a relationship.
- Michael James.