Luck 是名詞，意為「運氣；幸運，好運」，其後往往接介系詞 in 或 with 再接人事物來表示在某人事物上或對某人事物的運氣；lucky 是形容詞，意為「幸運的，運氣好的」。例如：
- Bruce always wears a charm that he thinks brings him good luck. (布魯斯總是戴著一個他認為會給他帶來好運的護身符)
- John seems to have had a lot of bad luck in finding a job. (約翰找工作時似乎碰到許多倒楣的事情)
- My luck held/lasted and I found a gas station just in time. (好運與我常相左右 / 好運一直伴隨著我，我即時找到一處加油站)
- A lucky person won the first prize in the competition. (一位幸運兒贏得了這項比賽的首獎)
- You’re lucky to work for such a nice company. (你能在這麽好的一家公司工作真是幸運)
- A: I got promoted yesterday. (A：我昨天升官了)
B: Lucky you! (B：你真是幸運！)
Luck 係不可數名詞，其前不可使用不定冠詞 a/an 且沒有複數型，但可以使用 any, some, much, a bit of 或 a lot of 來表示運氣的程度。例如：
- It was pure/sheer luck that they found the house. (他們找到那棟房子純屬運氣) (正)
It was a pure/sheer luck that they found the house. (誤) - Their luck is bound to run out sometime. (他們的運氣終將用完) (正)
Their lucks are bound to run out sometime. (誤) - Have you had any luck with finding a job? (你找到工作了嗎？)
- He has had much luck with girls. (他的女人緣極佳)
- With any luck (or with a bit/piece/stroke of luck), I’ll be a dentist next year. (幸運的話，明年我就當牙醫了)
由於 luck 為不可數名詞，因此泛指時，其前不可有定冠詞 the。例如：
- Sometimes it’s a matter of luck whether we are successful. (有時我們能否成功要靠運氣) (正)
- Sometimes it’s a matter of the luck whether we are successful. (誤)
中文的「祝你好運」可用 Good luck, (The) best of luck 和 I wish you luck 來表示。這三句都很常用且是固定用語，有人將 best of luck 說成或寫成 best luck 是錯的。例如：
- Good luck! (祝你好運！)
- I wish you luck! (祝你好運！)
- I wish you luck in your driving test! (祝你通過駕照考試！)
- I wish you all the best of luck! (祝你一切順心如意！)
- Good luck in your job interview! (祝你求職面試順利！)
- The best of luck in/with your exams! (祝你考試順利！) (正)
The best luck in/with your exams! (誤) - I think you’re taking a big risk, but anyway, best of luck! (我認為你冒很大的風險，但不管怎樣，祝你好運！) (正)
I think you’re taking a big risk, but anyway, best luck! (誤)
英文沒有 best luck 的說法，但 (除 good luck 外) 卻有 better luck 和 worst luck 的說法。例如：
- Better luck next time! (祝你下次運氣好一點！)
- Worse luck! (真倒楣！)
- I’ve got to work on Sunday, worst luck! (我星期天得加班，真倒楣！)