If you have difficulty distinguishing the World Bank from the International Monetary Fund, you are not alone. Most people have only the vaguest idea of what these institutions do, and very few people indeed could, if pressed on the point, say why and how they differ. Even John Maynard Keynes, a founding father of the two institutions and considered by many the most brilliant economist of the twentieth century, admitted at the inaugural meeting of the International Monetary Fund that he was confused by the names: he thought the Fund should be called a bank, and the Bank should be called a fund. Confusion has reigned ever since.

The attached document explains, in detail the difference.

Source: http://www.imf.org/external/pubs/ft/exrp/differ/differ.htm