In university we call it "semester", this word.
In school there is a Russian word which means "half a year" and another Russian word which means "quarter". So it is 2 or 4 of them, depending on how you count:)
There are vacations in between.
Summer vacation in my high-school started about 20 May and ended 1st september. I don't know what it is now.
Lessons are 6 days a week... And about 5 lessons a day in high school. This is the main difference with China: more free time.