This is one of those ones that's a tragedy. Biweekly "should" always mean every two weeks. Twice a week is "semi-weekly", aka every half a week.

But regardless of what it "should" mean, people use it wrong often enough that you have to check every time, not because the word is ambiguous, but because people are often mistaken.

It's a shame, but it's part of human communication 😅

There's also semi monthly, which is two times a month, as opposed to every two weeks, which is what biweekly is

Check the podcast episode “A Problem Squared - 121 = Bi-annuals and Diagonals”. In it, Matt and Beck discuss what these terms even mean, and propose a solution.

Fortnightly already exists as a term though, why would biweekly mean the same thing?