noun
the earth below; the ground below
Refers to the world or ground below a vantage point, such as from a high place or an aircraft.
飛行機から見ると、下界はまるで模型のようだ。
From the airplane, the world below looks just like a model.
noun
this world; the earthly realm
Buddhist term contrasting the human world with heavenly realms or the Pure Land.
仏教では、下界は苦しみの多い場所とされる。
In Buddhism, this world is considered a place of much suffering.
Compound of 下 (under, below) and 界 (world, realm). The Buddhist sense is a calque from Sanskrit or Chinese Buddhist terminology.