Practitioners have advanced and regulators have accepted a financial risk management technique called value at risk (VaR), which examines the tail end of a distribution of returns for changes in exchange rates to highlight the outcomes with the worst returns. Banks in Europe have been authorized by the Bank for International Settlements to employ VaR models of their own design in establishing capital requirements for given levels of market risk. Using the VaR model helps risk managers determine the amount that could be lost on an investment portfolio over a certain period of time with a given probability of changes in exchange rates.
Source:wikipedia