Does 'bimonthly' mean 'twice a month' or 'every two months'?
Unfortunately it means both! In the publishing industry, though, it's used fairly consistently to mean 'every two months', so that a bimonthly magazine is generally one that's issued every two months. The same ambiguity affects biweekly and biyearly. If you want to be absolutely clear, it's best to use a phrase such as 'twice a week' or 'every two years'.