When academic year starts and ends?

In most cases the academic year at Polish universities consists of 2 semesters of 15 weeks duration each. 
Fall semester starts in the beginning of October and lasts till mid-February, with two-week break for Christmas holidays and with a one-week vacation period in February. Spring semester starts in mid February and lasts till the end of June, with one-week break for Easter holidays. Summer vacation lasts from the beginning of July to the end of September.