Annual or annually.
Once every year.
Each/every/once a year.
Biannual describes something that occurs twice a year, once every half year.
once every year
Usually those days are called holidays.
Once.
The letter 'M'.
once every year
The letter E (once in a minute, twice in a week, and once in a year)
The letter 'M'.
The Moon rotates once every 24 hours
It means per year, or every year. The word annually means once per year or yearly. If you see your doctor for a physical on an annual basis then you see the doctor for a physical annually.