An overnight indexed swap (OIS) is an interest rate swap where the periodic floating rate of the swap is equal to the geometric average of an overnight index (i.e., a published interest rate) over every day of the payment period. A higher LIBOR-OIS spread is typically interpreted as indication of a decreased willingness to lend by major banks, while a lower spread indicates higher liquidity in the market. As such, the spread can be viewed as indication of banks' perception of the creditworthiness of other financial institutions and the general availability of funds for lending purposes. The historical average of the spread is around 10 basis points. (Source: Wikipedia)