A semester is a period of time in which academic courses are offered and completed. Several other terms can be used to refer to this period, including term, session, trimester, quarter, and block. A term can refer to a semester, trimester, or quarter and is often used in British English. A session can also mean a period of instruction, and it can be used interchangeably with semester or quarter. A trimester divides the academic year into three parts, while a quarter divides it into four. A block refers to a concentrated period of study, usually lasting a few weeks, in which students take one course at a time.