Definition
to encounter an unforeseen problem or get into unexpected trouble.
遇到（意外的）问题；陷入（意外的）麻烦
While sorting through old books, I ran across one that I thought I had lost.
在整理旧书时，我偶然发现一本我以为已经遗失的书。
He ran across an old friend on the street, which surprised him greatly.
他在街上偶然遇到一位老朋友，这让他非常惊讶。
While browsing the internet, I ran across an interesting article that I couldn't resist clicking on.
在浏览互联网时，我偶然发现一篇有趣的文章，忍不住点击进去。