means A half-year division of an academic calendar, typically lasting around 15 to 18 weeks, that organizes courses, exams, and the slow march toward a degree.

from Straight from Latin: semestris, meaning 'of six months,' stitched together from sex ('six') and mensis ('month'). So buried in the word is an old promise of half a year — which is amusing, since modern semesters rarely run a full six months. The term arrived in English via German university culture, where the academic year was carved into neat six-month halves.