O termo não é muito utilizado, mas não designa o ensino médio, e sim o "junior high" (da 6ª à 8ª série, geralmente), o que, no Brasil, é o fim do ensino fundamental.

http://en.wikipedia.org/wiki/Secondary_education

United States: high school (usually grades 9-12 but sometimes 10-12, it is also called senior high school) is always considered secondary education; junior high school' or 'middle school' (6-8, 7-8, 6-9, 7-9 or other variations) are sometimes considered secondary education.

Secondary education is the stage of education following primary school. Secondary education is generally the final stage of compulsory education. The next stage of education is usually college or university. Secondary education is characterized by transition from the typically compulsory, comprehensive primary education for minors to the optional, selective tertiary, "post-secondary", or "higher" education (e.g., university, vocational school) for adults