secondary school

Short definition from Wiktionary

Noun

1. 1
   A state school attended between the ages of 11 and 16 or 18 between primary school and university.
2. 2
   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.
3. 3
   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).