noun
on-season; peak season; in season
Refers to the busiest or most popular period for tourism, business, or seasonal products. Often contrasted with オフシーズン.
Antonyms: オフシーズン
夏は観光のオンシーズンで、ホテルが高い。
Summer is the peak season for tourism, and hotels are expensive.
この果物はオンシーズンになると安くなる。
This fruit becomes cheaper when it's in season.