Fed Funds Futures are offered by the Chicago Board of Trade and allow you to speculate on what the Federal Reserve will do with interest rates. The Federal Funds Rate is the interest rate which private banks charge eachother for overnight loans of excess reserves.
The Fed Funds Futures contract symbol is ZQ. Each contract allows you to control $5 million and is cash settled. The tick size is $20.835 per 1/2 of one basis point.
See also: 30 Day Federal Funds Futures (ZQ)