A subsidy is a allocation of money by a government to a organization or service to help pay for its costs. This is generally done for such things which benefit the public and do not make sufficient money on their own.
In 2372, First Minister Shakaar Edon's adjutant Sarish Rez suggested that Shakaar mention his recent increase of transit subsidies to the crowd gathered on Deep Space 9's Promenade to see him. He also asked Shakaar to mention that, as a result of the subsidies, the cost to travel between Bajor and Deep Space 9 should begin to drop within a few months. (DS9: "Crossfire")