A "concession" refers to something that is given or granted as a benefit or privilege. Similarly, an "incentive" is something that is offered to encourage or motivate someone to do something or to act in a certain way. In this case, the tax rebate is given to civil servants, which serves as an incentive or encouragement for them to continue working or to reward their service. Both "concession" and "incentive" imply a positive benefit or advantage provided to someone.