To encounter or run into something/someone unexpectedly; to be confronted with (an accident, difficulty, etc.).
山道で熊に遭遇したというニュースを聞いて驚いた。
I was surprised to hear the news that someone encountered a bear on a mountain trail.
プロジェクトは予期しない問題に遭遇し、計画を見直す必要が出てきた。
The project encountered unexpected problems and it became necessary to revise the plan.
昔の友人に駅で偶然遭遇した。
I ran into an old friend at the station by chance.