The most important or intense scene/stage/phase of an event, story, or task — the climax or turning point.
映画の山場では観客が息をのんだ。
At the film's climax, the audience held their breath.
交渉の山場を迎え、両者は真剣に話し合った。
Reaching the critical moment of the negotiations, both sides discussed matters seriously.
この試合の山場は後半の逆転シーンだった。
The turning point of the match was the comeback in the second half.
論文の山場は結論部分で、説得力を持たせることが大切だ。
The crucial part of a paper is the conclusion; it's important to make it persuasive.