To cancel a debt or an amount of money that is owed, considering it as a loss. The company decided to write off the bad debt after several failed attempts to collect it.
To dismiss someone or something as insignificant or unworthy of consideration. Many critics wrote off the film as a failure, but it later gained a cult following.
To damage a vehicle so badly that it is not worth repairing. After the accident, the insurance company decided to write off the car.