When a user unfriends someone on Facebook, as of 2014, the user no longer appears on the other's friend list. Both users also may not see certain content on the other's Facebook profile, assuming the content is not set to public view.
Besides limited viewing access on content, users who are no longer Facebook friends cannot post on each other's Facebook wall. Facebook also stops sending notifications about the other person's activity. A user may also opt to block a specific person, which prevents the latter from finding the former. Facebook does not notify users when they have been unfriended or blocked. Besides unfriending and blocking, Facebook offers privacy tools to control the content friends are allowed to see.