biweekly: happening or appearing every two weeks or twice a week. Cambridge Dictionary
In the following news articles, What the author mean by "bi-weekly"? if it is mean "two weeks" or "twice a week", Why doesn't they use a specific term to make it clear for readers?
Niantic was, by its own admission, caught off-guard by the sheer popularity of Pokemon Go, but it has pledged to continue supporting the game with bi-weekly updates. BBC
She's lived on Brexit Street for 18 months now but knows no-one. She only goes out to walk to her bi-weekly English lessons or to the drop-in centre round the corner. BBC
Best Answer
In biweekly the prefix bi- applies to the week rather than to the events that occur, therefore giving the sense of “every two weeks”.
In the meaning of "occurring two times a week", the term may appear chiefly in British English to be used when the context allows to clearly differentiate (as was shown in the previous answer) between the two meanings--occurring every two weeks or twice a week.
In situations where there's a possibility of any ambiguity, for the sake of clarity, it is recommended to use "twice a week" or "once every two weeks" accordingly instead of biweekly.
In some parts of the UK to describe an event happening once every two weeks, the term "fortnightly" is also common.
The source.