A semester is one of the two main parts that divide the school year at many middle schools, high schools, and colleges. Each semester typically lasts about 15 to 18 weeks, with one running from late August or September through December, and the other from January through May or early June.

Schools use semesters to organize learning into manageable chunks. At the end of each semester, students take final exams and receive report cards or transcripts showing what they've learned. Some classes last just one semester, like a fall photography course, while others continue for the full year. When someone says they're taking algebra “first semester,” they mean the fall term.

Not all schools use semesters. Some divide the year into trimesters (three parts) or quarters (four parts). The semester system gives students and teachers a natural breaking point to assess progress, complete courses, and start fresh with new material or even new classes.