Residuals, almost always in the plural, are the extra payments an actor, writer, or musician gets when their work is shown again — a TV rerun, another play on a streaming service, a commercial that airs once more. The first cheque is for making the work; residuals are for each later use. This is show-business English, especially American. You will not hear a shopkeeper use it. Though actually, some people loosely call any leftover royalty a residual. Do not mix this money sense with residual as an adjective meaning “left over” — same family, different job. In ordinary Taiwan talk you are more likely to hear 重播費 than this English word.