An academic term (or simply “term”) is a portion of an academic year, the time during which an educational institution holds classes. The schedules adopted vary widely. A semester system divides the academic year into two terms, which are usually 14–20 weeks each. A trimester system divides the academic year into three terms which can be as short as eight weeks or as long as 16 weeks each. A quarter system divides the academic year into four terms, up to 12 weeks each, and generally counts the summer as one of the terms. The word quadmester or quadrimester is occasionally used to mean either four months or (more commonly in modern American usage) a quarter of a year. In most countries, the academic year begins in late summer or early autumn and ends during the following spring or summer. In Northern Hemisphere countries, this means that the academic year lasts from August, September, or October to May, June, or July. In Southern Hemisphere countries, the academic year aligns with the calendar year, lasting from February or March to November or December. The summer may or may not be part of the term system.