clear autumn day; fine fall weather
Refers to a calm, sunny day in autumn, often with a sense of pleasant, mild weather.
今日は秋日和で、散歩が気持ちいい。
Today is a clear autumn day, perfect for a walk.
Compound of 秋 (autumn) and 日和 (weather, often fine weather). The reading びより is a rendaku form of ひより.