Answer:
Overdraft is a facility wherein a customer can withdraw money from his account even if he does not have sufficient balance to cover for it. He would have to eventually return the money to the bank but still he can take cash for his requirements anytime he wants.
You will be paying an interest equivalent to the money that you have taken from your OD account for as long as you haven't repaid the money in full. Also the bank will charge you an annual fee for providing the OD facility.