(covers information from several alternate timelines)
A tax was a fee levied by a government that paid for public institutions and programs. It could be based on income, property ownership, purchases of goods or services, or licenses and permits.
One supposed reason for his exile from Cardassia that Elim Garak told Doctor Julian Bashir was that he had failed to pay his taxes and had been punished by the Finance Ministry. (DS9: "Improbable Cause")
In 2372, the Ferengi imposed a six percent tariff on woolen goods they traded with the Karemma, claiming that the tax was added to help offset the "lost income of Tarkalean sheep herders." (DS9: "Starship Down")
One of the reforms that Grand Nagus Zek instituted in the mid-2370s was the introduction of progressive income tax in the Ferengi Alliance, in order to pay for new social programs such as retirement benefits and universal health care. This progressive income tax was introduced to all areas of Ferengi life, as even bribes were made tax deductible. (DS9: "The Dogs of War")