The season of heavy or frequent rain (the rainy season).
日本の梅雨は雨季にあたり、湿度が高くなる。
Japan's rainy season (tsuyu) is a rainy period when humidity increases.
旅行は雨季を避けたほうがいい。
It's better to avoid traveling during the rainy season.
熱帯地方では雨季と乾季がはっきり分かれていることが多い。
In tropical regions, the rainy season and the dry season are often clearly distinct.