senior high school
US /ˌsiː.njər ˈhaɪ skuːl/
UK /ˌsiː.njər ˈhaɪ skuːl/

1.
a high school for students in the higher grades, typically grades 10-12 or 11-12, preparing them for higher education or vocational training
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My brother is currently attending senior high school.
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After graduating from senior high school, she plans to go to university.