What Do We Mean in Our Current Banking System When

What do we mean in our current banking system when we say that a currency is "fractionally backed"?

A) Banks have many more claims outstanding against them than they have reserves available to pay those claims.
B) The currency is partially backed by the nation's supply of gold.
C) A bank's currency is fractionally backed by its supply of gold.
D) All paper currency is convertible to gold.
E) Banks maintain a fixed fraction of their outstanding deposits as cash deposits with the central bank.