summer vacation; summer holidays
Refers to a formal summer break, typically from school or work. More formal than 夏休み.
The university's summer vacation lasts through August.
The office will be closed during the summer holidays.
夏休み is the common, everyday term for summer vacation, while 夏期休暇 is more formal and often used in official or academic settings.
Compound of 夏期 (summer period) and 休暇 (holiday, vacation).