noun
third year of junior high school; third-year junior high school student
Abbreviation of 中学校３年(生). Used in educational contexts to refer to the grade or the student.
中３の夏に塾に通い始めた。
I started going to cram school in the summer of my third year of junior high.
うちの子は来年中３になります。
My child will be a third-year junior high school student next year.
Abbreviation of 中学校３年(生), combining 中 (from 中学校) with ３ (third year).