noun
beautiful clear weather; cloudless sky
Refers to a perfectly clear, bright sky, often with a sense of ideal Japanese weather. Can be used literally or figuratively to describe a situation free of trouble.
今日は日本晴れで、富士山がよく見える。
Today is a beautiful clear day, and Mt. Fuji is clearly visible.
運動会は日本晴れの空の下で行われた。
The sports day was held under a cloudless sky.
Compound of 日本 (Nihon, 'Japan') and 晴れ (hare, 'clear weather'). The term likely originated from the idea that such perfectly clear skies are especially characteristic of Japan, or from a sense of national pride in beautiful weather.