Rollover refers to extending the settlement date by which an open position must be executed.
While in currency trading the rollover is two business days, in margin trading open positions must be closed at 22:00 GMT every day and re-opened on the next trading day.
Rollover is agreed on through a swap contract which comes at a cost or gain for traders. PFH MARKETS does not close and re-open positions but debits/credits trading accounts for positions held open overnight, depending on the current interest rates (LIBOR/LIBID with added mark-up).