If you say that something is a figment of someone's imagination, you mean that it does not really exist and that they are just imagining it.
例句
The attack wasn't just a figment of my imagination.袭击可不是我凭空想象出来的。
英汉词典释义
n.
虚构的事物
a figment of the imagination虛构的事
臆造的事物;虛构的事
Doctor, are you suggesting the pain is a figment of my imagination?医生,你是说这疼痛是我想像出来的喽?The figure vanished as silently as if it had simply been a figment of her imagination.那个人影无声无息地消失了,仿佛一切只是她的凭空想像。