[usually singular] used to refer to a person, thing, etc. when you do not know their name or when you are talking in a general way （指叫不上名字的人、物，或泛指）某某人（或事物）
What would you say to Mrs So-and-so who has called to complain about a noisy neighbour?
要是哪位太太嫌邻居太吵闹，打电话投诉，你怎么跟她说？