Swap fee refers to the interest earned or paid by traders when they hold a position overnight. This interest is calculated at 22:00 London time. The rate of swap fee depends on the direction of the trader's position and the interest rate differential between the relevant currencies. For instance, if the interest rate for Pound is significantly higher than that of the Japanese Yen, a trader holding GBP/JPY in a long position can earn interest, while a trader holding GBP/JPY in a short position will incur interest charges.