1. The night and day are the same length
2. We change our clocks for daylight savings
3. Change the batteries in your smoke detectors
4. Go for a dental check up
5. Solar/Lunar eclipse
The answer is 'Biennial'.
What happens biannual
If something is biannual, it happens twice a year.
An event of some sort that happens twice a year.
.
.
the letter E
Biannual or semiannual.
The letter E. wEEk and yEar.
the letter E
Biannual
equinax
The letter e.
The letter E appears twice in wEEk, one in yEar, but not in day.