Facebook is a vast community consisting of approximately 2 billion users, and over time it’s easy to amass a large number of “Facebook friends”.
As your friends list grows, it’s inevitable that some of your friends will deactivate their accounts for some reason but never got around to actually deleting it.
The thing is, when a friend’s account is deactivated that person isn’t automatically removed from your friends list.
Those friends who are no longer active on Facebook are called “ghost friends”.