High school is called "high" school because it is one that covers the latter years of compulsory education, providing advanced or elevated levels of learning compared to elementary or middle school.
The term "high" suggests a higher academic level and a more specialized curriculum.
Additionally, high schools often prepare students for higher education or entry into the workforce. The usage of "high" in this context is likely derived from the Latin word "altus," meaning "high" or "deep." Over time, the term has become ingrained in the educational system, symbolizing the elevated and more challenging nature of the educational experience during these crucial years.