The term rollover is used exclusively for FX positions. Rollover fees are charged on FX positions held overnight. Every day at 4PM 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.