It's by some means the amount of (internationally-recognisable) reserves securing the money supply at a given moment of time. In retrospective, gold was used to determine the money base.
Since the second half of eighties the notion of amorphous "reserves" underlying the money base was consistently presented as an axiom-type statement, which, however contradicts the actual incidents underlying the separation of current monetary system from gold.
Many economists fear that money base is increasingly diluted, thus the quantifieable "reserves" in the world monetary system today are in essence amount of (mostly) unsecured debt.
Please refer to economic discussions relating to gold standard and the system of world currencies for further information about money base - dependencies/trends
Monetary policy is carried out by the Federal Reserve Board and the Federal Open Market Committee, the 12-member committee (including all 7 governors of the Federal Reserve Board), which directs the open market purchase and sale of government securities for the 12 Federal Reserve Banks.
Monetary policy is generally referred to as either being an expansionary policy, or a contractionary policy, where an expansionary policy increases the total supply of money in the economy, and a contractionary policy decreases the total money supply.
Monetary policy was seen as an executive decision, and was generally in the hands of the authority with seniorage, or the power to coin.
Monetarybase growth was quite high during the years of the largest banking crises.
Monetary forces explain the severity of the nominal decline, but it seems necessary to look at labor market policies and other interventions to explain why the real reaction to the nominal decline was so sharp.
Based almost entirely on Hoover's opposition to the dole (note that evidence of negative consequences on British economy were already evident), and the fact that FDR took the policies considerably further.