這四個詞都有「假期」的意思，但具體含義有所不同。holiday , vacation,leave是名詞，
off是副詞。具體區別如下：
1.holiday一般表示時間可長可短的假期，為可數名詞。與季節連用時多用複數;與數詞連用時只表示次數。
We spent our summer holidays in the countryside.我們在鄉下過的暑假。
We have had three holidays since the beginingofthe year.
從今年年初開始，我們已經有三個假期了。
a holiday of three days=a three days' holiday三天的假期
2.vacaion一般表示比較長的假期，多指大學的假期、法庭的休庭期。至於寒、暑假，英國人喜歡用: summer/ winter holidays, 美國人喜歡用: summer/winter vacation, 區別不大。
We spent our summer holidays/vacation in the countryside this year.今年我們在鄉下過的暑假。
My dad is now on holiday/ vacation in Beijing.我爸爸現在在北京度假。(表示狀態)
Every year, we go to the island for holiday/vacation.
每年我們都去島上度假。
(表示目的,holiday/vacation用單數，前面不加冠詞，但可用on/for one'sholidays.
3.leave多指政府部門、機關事業單位、部隊等的休假。
ask for leave for three days請三天假
The worker asked for leave for two days to see a doctor.這個工人請了兩天的假去看病。
4.off是副詞，表示「休假、不工作、不上班」，多用於名詞後作定語。
The teacher will give me five days off. 老師將要給我五天的假。
The worker asked for two days off to see a doctor.這個工人請了兩天的假去看病。