A mountain pass or the highest point on a mountain road; a ridge or passage through the mountains.
峠を越えると景色が一変した。
After crossing the pass, the scenery changed completely.
冬は峠道が凍結して危険だ。
In winter the mountain pass roads freeze and are dangerous.
自転車で峠に挑戦するのが趣味だ。
I enjoy challenging mountain passes by bicycle.
A peak, crisis, or the most difficult/critical point of something (e.g., the worst phase of an illness or the climax of a situation).
彼の病状はようやく峠を越えたらしい。
It seems his condition has finally passed the worst part.
計画は今が峠だ、ここを乗り切れば順調になる。
The plan is at its toughest point now; if we get through this, things will go smoothly.
夏の暑さも峠を越したようだ。
It seems the peak of summer heat has passed.