That seems backwards to me. Mainly because if you move it to years instead of weeks, something that happens twice a year happens in half a year (semiannual) while something that happens every other year happens in 2 years (biannual).

Of course, I guess you you argue that it isn’t much time for the thing to happen, but how many times it does happen. The shareholders meeting happens in January and July, so it happens twice in a year, and it should be semiannual. This is because it happens is semi-year, or 6 months. But you could argue that it happens twice in a year, so has bi-annually.

I realized I may have talked out of my original point, but I feel like my initial comment (semiannual is 6 months, and biannual is 24 months) is easier to understand.