prefectural high school; public high school
A high school operated by a prefectural government. In Japan, these are the most common type of public high school, as opposed to municipal or national schools.
He attends a local prefectural high school.
The entrance exam for prefectural high schools will be held next month.
公立高校 is a broader term for any public high school (including prefectural, municipal, and national), while 県立高校 specifically refers to those run by a prefecture.
私立高校 is a private high school, as opposed to a public one like 県立高校.
Compound of 県立 (prefectural) and 高校 (high school).