noun
well bottom; narrow place
Literally the bottom of a well; also used figuratively for a confined, narrow space or limited perspective. Often appears in the idiom 井底の蛙 (a frog in a well).
井底の蛙、大海を知らず。
A frog in a well knows nothing of the great ocean.
彼は井底のような狭い世界で育った。
He grew up in a narrow world like the bottom of a well.
Compound of 井 (well) and 底 (bottom). The figurative sense derives from the classical Chinese idiom 井底之蛙 (a frog at the bottom of a well).