A secondary school is an educational institution that follows primary school and provides secondary education, typically for children aged between 11 and 18 years old. Secondary education is usually divided into two stages:

• Lower secondary education (around ages 11 to 14), which builds on primary education with a more subject-oriented curriculum.
• Upper secondary education (around ages 14 to 18), which prepares students for tertiary education or vocational work and offers a broader range of subjects.

In some countries, secondary education may be split into middle school and high school. For example, in the U.S., middle school covers grades 6–8 or 7–8, and high school covers grades 9–12. In the UK, secondary school typically covers ages 11 to 16 or 18. Secondary schools aim to prepare students either for higher education (college or university) or vocational opportunities. The exact age range and structure vary by country, but students usually complete secondary education by age 16 to 18, after which they may proceed to work or further studies. Different countries have various names and structures for secondary schools, but the concept is generally the phase of education between primary school and higher education or employment. The size and organization of secondary schools can vary widely depending on local educational policies and community needs. In summary, a secondary school is the educational stage between primary school and higher education or vocational training, typically serving students aged 11 to 18.