Refers to a particular season or time of year, often in the context of weather, climate, or seasonal greetings. Common in set phrases like 時候の挨拶 (seasonal greeting).
I write a seasonal greeting at the beginning of a letter.
At this time of year, the weather is unstable and it's easy to get sick.
unseasonable; out of season
Compound of 時 (time) and 候 (climate, season). The combination has been used since classical Chinese to refer to seasonal weather and appropriate times.