A surtax is an extra tax added on top of the normal tax — usually charged only on income above a certain level, or on a particular thing the government wants to tax more. The point is that it does not replace the ordinary tax; it sits on top of it. So someone earning a lot might pay the standard income tax on everything, plus a surtax of a few percent on the part above the line. It can also be a verb, though that is much rarer: to surtax something is to put that extra tax on it. This is a formal word from news, economics and government, not from daily conversation — even people who pay one would more likely say "the extra tax" or name it directly. You will meet it most in reading: business news, textbooks, articles about the rich and the government.

附加稅（在原本的稅之上再多加的一層稅）