A donation was an amount contributed to a worthy cause.
In 2370, Quark encouraged Julian Bashir to throw a darts match against Miles O'Brien, as everyone was gambling on Bashir to win. If he defeated O'Brien, the Ferengi would make no profits, meaning there would then be no donation money left to buy blankets for the children aided by Bajoran War Orphans Fund. Bashir refused to throw the game. (DS9: "Rivals")
In 2375, Worf, Miles, and Julian all went to fight a battle in a deceased Jadzia Dax's name so that she could enter sto-vo-kor. Quark, believing their mission to be foolhardy. questioned whether they could just make a donation in her name or bribe someone instead. Bashir assured him it didn't work that way. (DS9: "Image in the Sand")