請問a de facto tax是甚麼？

De facto is a Latin expression that means "of the fact" or "in practice" but not ordained by law. It is commonly used in contrast to de jure (which means "by law") when referring to matters of law, governance, or technique (such as standards) that are found in the common experience as created or developed without or contrary to a regulation. When discussing a legal situation, de jure designates what the law says, while de facto designates action of what happens in practice. It is analogous to and similar to the expressions "for all intents and purposes" or "in fact".
De facto tax could be translated as 實質性稅項。For example, the Government may levy an environmental charge on bleaching of garments, as the wasting water will pollute the river. Apparently, this is a charge but, if you look at this from another angle, this maybe regarded as a tax levied by the government on this industry. So, a number of instances that environmental tax is being used instead of a charge. 把費改為稅