Hard to believe, we know. To simplify it, a day is defined by the time it takes for the sun to get to the same part of the sky as it was the day before. It takes more than one spin to complete a day, because we have to make up for the distance weve moved around the sun. If youre still confused, see the source below.
source: https://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970714.html (subheading: the suns path in the sky)