From Encyclopedia Jr, free information reference for Kids
Biweekly is a reference to an event that occurs once every two weeks. An example of a biweekly event would be the production of some magazines that have lower subscription numbers or budgets than the more common weekly printings, but a content or circulation making the more usual monthly printing unfeasible or less appropriate.
The term is sometimes misused, particularly in British English, to mean an occurrence which occurs two times every week, though this is properly referred to as "semi-weekly". The numerical prefix bi means "two".
There is some debate on the subject. OED and Merriam-Webster offer descriptive definitions both of two times per week and once every two weeks,[1] though in the context of publishing, only the latter usage is ever correct.[2]