Rolling spot FX contracts are subject to funding adjustments (debits or credits) if you keep a position open at the end of each business day, after 10pm London time (normally 5pm EST). Funding adjustments are based on the current tom-next rate for the currency pair you are trading.
Tom-next shows, in pips, the difference between the interest paid to borrow the currency that is being notionally sold, and the interest received from holding the currency that is being notionally bought. IG takes the tom-next rate received from its brokers and applies an admin fee of 0.5% p.a. Depending on the direction of the position, and the currencies involved, this adjustment could be a credit or debit.