Senior secondary education

The senior secondary years are the years of later adolescence corresponding to the later part of secondary education. Although definitions vary, the senior secondary years are sometimes defined as being from approximately age 15 to age 18. The term generally includes eleventh grade and twelfth grade, and may sometimes also include tenth grade.
The senior secondary years often involve a difficult transition from the world of the child to that of the adult. In many countries, school attendance is no longer compulsory in the senior secondary years. 
The term "senior secondary" may also be used to refer to any institution that covers the upper part of secondary education, such as a high school.
Australia.
In Australian education, the senior secondary years are the last two years of secondary education, years 11 and 12. The Senior Secondary Certificate of Education (SSCE) is the graduation certificate awarded to most students in Australian high schools. The name and the curriculum of the certificate varies between each state and territory. Some institutions have also traditionally included year 10. Under the Australian Curriculum implemented in the early 2010s, the senior secondary years have a separate curriculum from the curriculum that runs from through year 10.