<p>Biweekly has two conflicting meanings. Historically it refers to an event that occurs every two weeks. In current usage, it can also refer to an event that occurs twice in a given week. The term fortnightly can be used less ambiguously for the first sense, with a two week interval equivalent to one fortnight. Semi-weekly, similarly, can be used for the second sense; every half week or twice a week.
There are fifty-two weeks in a year of twelve months, making for a possible 26 (or 104) biweekly events in a year. (This is a greater number than if such events were held twice a month, due to the fact that most months have more than four weeks (28 days). However, biweekly is often thought of incorrectly as twice a month. Twice a month is called "semimonthly" or "bimonthly", not biweekly.)</p>