In India, in the time of British rule, memsahib was how people spoke to or spoke about a European woman — often the wife of a British official. It is not a word you need for today’s English in Taiwan, or in most English-speaking countries; you will meet it in older books, films, and history. Though actually, the feeling around it is mixed. To some it was simply “madam”; to others it carries the whole stiff world of empire, servants, and distance. It sounds old now, and in modern talk it can feel colonial or even mocking, so you would not use it of a woman today unless you were quoting that old world. A European man in the same setting was a sahib.