The term rollover is used exclusively for FX positions. Rollover fees are charged on FX positions held overnight. Every day at 4:00 PM GMT each account is charged or credited with the rollover fee for FX positions held the previous night.
The rollover is calculated as (current notional value x * rate * days) / 360.
They are published on a daily basis. If the overnight rate is positive, it will be added up to your account. If the rate is negative, you will be charged with the stated amount.