one of two divisions of an academic year
"She decided to take a break after finishing her first semester at university."
half a year; a period of 6 months
"The professor announced that the semester would end in June after covering all the final chapters."
Half of a school year (US) or academic year such as fall or spring semester.
"She decided to take an extra class during her summer break so she could finish all the requirements for the spring semester early."
In plain English: A semester is one of the two main parts that make up an academic year at school or college.
"She plans to finish her degree in two semesters."
Usage: In American English, a semester is one half of an academic year, typically divided into fall and spring terms. Unlike the British trimester system which splits the year into three parts, semesters are standard in most US colleges and universities.
The word semester comes from the German term Semester, which was borrowed into English via New Latin. It originally described a period lasting six months, combining roots for "six" and "month."