Twice a week. OR
Every other week. OR
It really doesn’t have any meaning because it could mean either of the two ideas above.
Since we have the word “fortnightly” to mean every two weeks, it makes sense for “biweekly” to mean twice a week.
Bi-weekly = every two weeks. Semi-weekly = twice a week.
Bi-weekly means every two weeks to me. Semi-weekly would be twice a week. I suspect there would be some disagreement about the former but not the latter.
In America, we don’t use “fortnight.” Biweekly means every two weeks much more often than it means twice a week.
We do in my America.
Granted, people look at me funny when I use it, but I’m used to that.
Biweekly = twice a week.
Fortnightly = once a fortnight.
Nowadays it means both, just like with biannual.
On a related note, whenever someone uses “peruse,” I have to ask him/her what he/she wants to convey since now it can mean to read carefully or to skim. Of course, it meant to read carefully when I learned the word in 9th grade English.
I read “biweekly” as every-other week.
I read “bimonthly” as twice a month.
I think both are ambiguous, but I have a lot more stuff that happens about twice a month than that happens every other month or twice a week. 
I used to work in a job that required a lot of discussion about the frequency of people’s paychecks.
It infuriated me when my coworkers would use “bi-weekly” to refer to “every two weeks,” and “bi-monthly” to refer to “twice a month.” I got the stink eye more than once in training for asking the trainer: “Do you mean *semi-*monthly?”
Every two weeks.
‘Twice a week’ is an abomination against everything that even vaguely resembles logic.
So basically, they were synonyms.
So in your America only a few random people say “fortnight,” and they get funny looks when they do?
I think we live in the same America. 
no, some years you get an extra paycheck if your pay is bi-weekly, but you always get 26 paychecks if you are paid bimonthly. 
It’s funny this thread is made because I actually had this thought earlier today because bi-weekly, to me, means twice a week. Bi-monthly is twice a month…and so on. But when I said it at my last job they scolded me for improper use. But I still want to use it that way.
No, it can’t. No more than “bisexual” means you like having sex with men only, but twice as much.
This is the correct answer. The only correct answer.
… your calendar has 13 months?
Going by the dictionary meaning I learnt - Bi-Weekly would mean every two weeks.
Same as “biannual” means every second year.
But I would never use it - simply because too many people will get it wrong.
Would prefer “fortnightly” (yes it is common here) or “every second week”.
If I am using it to refer to years (I am in the exhibition industry, where trade fairs are commonly held biannually) I would use a construction like “alternate years” or “every other year”
The other one where you have to be careful -
What is the difference between “feet squared” and “square feet”?
Would I be right to say that 100 feet squared is 100 feet on each edge (i.e 10,000 square feet) while
100 square feet is actually 10’ x 10’ ?
weekly - every week
bi-weekly - every other week
bi-monthly - twice a month (1st and 15th ish)
Annually - once a year
Semi-annually - twice a year
bi -annually - every two years.
Its all very confusing.
lol, no, I just messed up.
If you get paid every two weeks, you get either 26 or 27 paychecks, depending on the year. So there are a few months when you get an “extra” paycheck. If you get paid twice a month, you get paid 24 times every year.
Because most large bills come once a month, many employees prefer being paid every-other week, because it’s sort of an easy way to “save up” a paycheck.
Every two weeks. End of discussion.