凯子 is a slang term originating from Taiwanese Mandarin, used to describe a man who is easily tricked into spending money, often for romantic or sexual favors — essentially a 'sugar daddy' or 'dupe.' It carries a derogatory connotation and implies that the man is being taken advantage of. The word is not a direct equivalent of 'prodigal'; it specifically involves a power dynamic where the woman is the manipulator. Avoid using it in formal contexts.