中国的学校是这么排列的：幼儿园、小学、初中、高中，大学。 “中学”包含“初中”和“高中”

中学 包括初中， junior and senior high school 初中就是 junior high school 希望对你有帮助~

中学include junior high school，senior high school

From my view,中學 in Malaysia is refer to the whole secondary school period, but 初中 is part of them,It is between 13-15 years old, so 16-17/18 years old will study in 高中(high school).