Senior high school (abbreviation for 高等学校); the educational institution typically covering three years after junior high.
来年、高校に入学する予定だ。
I'm scheduled to enter high school next year.
高校の授業は専門的な内容が増える。
High school classes increase in specialized content.
高校生の通学時間は長い。
High school students have long commuting times.