정말 감사합니다

example - 휴일 : saturday, sunday, christmas, national holiday - 휴가 : summer vacation, day off

휴일 is a holiday as in a legal holiday (the way "holiday" is used in the US.) 휴가 is a vacation you would take from work. It may translate as "Holiday" in England or some other English speaking countries, but would be "Vacation" in the US. That's the usage I hear, but let the native Korean speakers give you their answer.