There's day and night.
We know the difference, in the day the sun is up and in the night the moon is up. 🌞 🌛
Then there's the word for a 24 hour period, not necessarily starting at 00:00.
In English that word is "nychthemeron". A clunky word. Other languages have better words.
We should create a new English word for it, for example "mero", "para" or "doba"