public high school
A high school operated by a prefectural or municipal government, as opposed to a private (私立) or national (国立) high school.
彼は地元の公立高校に通っている。
He attends a local public high school.
公立高校の学費は私立より安い。
Tuition at public high schools is cheaper than at private ones.
私立高校 is a private high school, while 公立高校 is a public high school run by a local government.
国立高校 is a national high school, which is rarer; 公立高校 is more common and run by prefectural or municipal governments.
Compound of 公立 (public, from 公 'public' + 立 'establish') and 高校 (high school, abbreviation of 高等学校).