Overnight Rate - Bank of Canada sets a target bandwidth for the overnight rate each month of +/- 0.25% around its target overnight rate: the Bank of Canada does not interfere in the overnight market so long as the overnight rate stays within its target band, but the Bank will use its reserves to lend or borrow in the overnight market to ensure that the overnight rate stays within its announced bandwidth.

GDP - is defined as the market value of all final goods and services produced within a country in a given period of time. It is also considered the sum of value added at every stage of production of all final goods and services produced within a country in a given period of time. GDP is the basically direct measure of the economy's health, and a stronger GDP means that the central bank will more likely to raise interest to curb inflation.  UK's GDP is released on a monthly basis although the figure is for quarterly reading. The first release is within 30 days of the end of the quarter (Prelim GDP), followed by the second release (Revised GDP) 30 days after the first release, then with the final release (Final GDP) almost 90 days after the end of the quarter...  

US GDP - GDP, which is defined (from wikipedia) as "the market value of all final goods and services produced within a country in a given period of time. It is also considered the sum of value added at every stage of production of all final goods and services produced within a country in a given period of time." GDP number has a direct effect on the Interest rate of the currency, it is one of the news indicators that affects FOMC's decision directly.  US GDP is release monthly in a quartely format.  The first release is called Advanced GDP, followed by Prelim GDP, then Final GDP; they are released within 30, 60, 90 days after the end of the quarter, with Advanced GDP being the focus of the market since it is the first release of the quarter.