How does slippage work?
The slippage feature acts as a protection for you if you don't want to get filled too far away from the last quote you saw.
Sometimes, because of different market factors, you might not get filled exactly at the price you wanted. So the slippage factor allows you to decide the limit for the amount to which the price can slip from what you expected. The order will not be executed if your slippage factor is exceeded.