What does "fool's paradise" mean? Is it an idiom?

Native speaker’s answer
Rebecca
Yes, It is an idiom. To live in a fool's paradise means to be happy because you do not know or will not accept how bad a situation really is. So it's kind of a feeling of false happiness. Ex: She indeed lives in a fool's paradise as she always dreams about making a huge fortune overnight. Ex: You must be in a fool's paradise if you think that it will rain at the time of such hot summers.