Basis is a multiplier used to calculate the total interest paid or received in a defined time period. It is typically used in accounting and valuation for bonds, swaps, dividends, project finance, and other investments with periodic cash flows. Basis is also known as the "day count convention" because it defines how days in a year are treated for calculation purposes in different parts of the world.

Daily Price
The notional is expressed in units per day, used for commodities. The price for the day is multiplied by the notional every day of the period then the daily amounts are netted. For example, an oil swap would pay on a daily basis as follows: if the period is 3 days long, the notional is 1,000 barrels and the prices are 20 on the first day, 21 on the second and 22 on the third day. Then, the payment at the end of the three days will be: 20 x 1000 + 21 x 1000 + 22 x 1000 = 63000.