summer vacation; summer holiday
Refers to a formal or scheduled summer break, often used in school or company contexts.
Summer vacation starts next week.
I plan to go on a trip during the summer vacation.
More casual and common for schoolchildren's summer break. 夏季休暇 is more formal and often used in official or business settings.
Compound of 夏季 (summer season) and 休暇 (holiday, time off).