Keyhole Friend

A person who you call a friend but you literally look at their life through a keyhole. This means you don't completely see their entire life, just whatever small piece you can see, or they allow you to see through the keyhole (social media like facebook, twitter, instagram or snapchat). The only reason this person isn't called an acquaintance is because it would seem rude to refer to them as such.

Jack: Hey Joe, are you and Kevin close.
Joe: Nope, we're keyhole friends, the most I know about him is he added that he changed his display pic four weeks ago.