Biweekly vs. semi-monthly

Biweekly means every two weeks — 26 paychecks a year. Semi-monthly means twice a month, usually the 15th and the last day — 24 paychecks a year. They sound interchangeable and are not: the same salary produces a smaller biweekly check than a semi-monthly one, and biweekly gives you two months a year with three paychecks.