A lot of my friends have been asking this to me so I’ll just go ahead and make a blog post for everyone. According to facebook:
If you block someone, they will not be able to find you in a Facebook search, see your profile, or interact with you through Facebook channels (such as Wall posts, Poke, etc.). Any Facebook ties you currently have with a person you block will be broken (for example, friendship connections, Relationship Status, etc.). Note that blocking someone may not prevent all communications and interactions in third-party applications, and does not extend to elsewhere on the Internet.
So in essence you become invisible to that person and there is no way he/she can add you back or search for you unless he/she makes a new profile.
Blocking a friend:
The blocking process is fairly simple and most of you already know it:
You just have to click on ‘Report/Block this Person‘ and check the “Block this person” and click on Submit.
Unblocking a friend:
Unblocking friend is a little different and is a bit difficult to find at first. Thats why people have been asking about that to me.
I’ll show you how to do it:
Go to your privacy settings (click here if you are already logged into facebook):
Click on ‘Edit your lists‘ under ‘Block lists‘.
You’ll be presented with your block lists. Click on ‘Unblock‘ next to the friend you want to unblock and click on ‘Confirm’. Thats it.