Time periods relating to Chinese holidays (暑假, 寒假 etc.)
假 means 假期 vacation, it also have 病假 sick days, and 请假 request a vacation/day off. 
寒假 暑假 is mainly for students and teachers.

For 暑假 it usually starts at late June, and ends at 1st Sep, it's about 2-3 months. For 寒假, it depends on the day of chinese new year, usually it starts 1 or 2 weeks before that, and last for 1 and a half months.