Assuming you all know "F/R" means "friend request", I'll continue on with the article.

Facebook released a tiny new feature to friend requests called "Mark as Don't Know". If you've been using Facebook for a while, chances are you've gotten a friend request from the same person that you either just don't want to add or you're positive you don't know that person.

Now, after ignoring a friend request, you have the option to mark it as so, and you will no longer receive friend requests from that person. A quiet feature, but a convenient one.