Money Is Often Said to Be "Socially Defined

Money is often said to be "socially defined." What does this mean?

A) That parliament has defined what money is.
B) That society defines what money is in terms of what it deems acceptable.
C) That the money supply includes all public and private securities purchased by society.
D) That only the Bank of Canada can supply money and this bank is owned by the public.
E) That a nation's money supply must be backed by something socially acceptable such as gold.