What is the meaning of Secondary_school?

In the UK and Ireland, a state school attended between the ages of 11 and 16 or 18.

The federally designated, graduation-separated classification of grades 9–12 (approximately ages 14–18), regardless of whether they are compiled together in one school or separate from the other grades.

School with education level between primary school and university.

Middle school; junior high school; a school that one attends between the ages of 12-17 (equivalent of grades 7-10 in North America, and years 7-10 in Australia).

Source: wiktionary.org