noun
daydream; waking dream; fantasy
Refers to a dreamlike state while awake, often involving pleasant fantasies or unrealistic thoughts. Similar to 白昼夢 (はくちゅうむ), but 白日夢 is a less common variant.
See also: 白昼夢
授業中、彼は白日夢にふけっていた。
During class, he was lost in a daydream.
その計画は単なる白日
That plan is nothing more than a fantasy.