Rollover is a charge or a payment that is applicable to the trading position(s) held over the monthly expiration date when a client trades futures CFD products such as Oil, VIX, etc.
This is because a futures contract has a set expiration date and if the client decides to continue holding the open position(s) over the expiration date, the old contract position(s) must be closed as the contract expires and new position(s) must be opened on the new futures CFD contract for the next month.
The monetary impact is largely nullified, as the changes in values of the open positions are offset by debit or credit adjustment made to the account. It appears on your account's trading statement as ‘Cash Adjustment-Rollover’.
If the client does not wish for the position(s) to be rolled over to the new contract month, then the client must close the position(s) prior to the rollover or the contract expiration date.