Roll over is a widely used term in the Forex trading world, and it stands for the carrying of positions to the next trading session. In case traders decide to hold positions overnight, their positions are "rolled over" to the next trading session.
This action is followed by a rollover interest swap, which is added or deducted from client's balance and calculated in accordance with the gap (negative or positive) between the trading pair's interest rates. Therefore, when a position is held overnight, an interest may be added or deducted from it according to the pair's swap rate. All swaps can be found at your trading platform for each currency pair, depending on the sort of position (Long/Short).