Debt ratings, risk and cancellation Risk free interest rate

Lending’s to stable financial entities such as large companies or governments are often termed "risk free" or "low risk" and made at a so-called "risk-free interest rate". This is because the debt and interest are highly unlikely to be defaulted. A good example of such risk-free interest is a US Treasury security - it yields the minimum return available in economics, but investors have the comfort of the (almost) certain expectation that the US Treasury will not default on its debt instruments. A risk-free rate is also commonly used in setting floating interest rates, which are usually calculated as the risk-free interest rate plus a bonus to the creditor based on the creditworthiness of the debtor. In reality, no lending is truly risk free, but borrowers at the "risk free" rate are considered the least likely to default.
However, if the real value of a currency changes during the term of the debt, the purchasing power of the money repaid may vary considerably from that which was expected at the commencement of the loan. So from a practical investment point of view, there is still considerable risk attached to "risk free" or "low risk" lending. The real value of the money may have changed due to inflation, or, in the case of a foreign investment, due to exchange rate fluctuations.
The Bank for International Settlements is an organization of central banks that sets rules to define how much capital banks have to hold against the loans they give out.