1 The duration of one rotation of the earth on its axis, with respect to the sun
day: time for Earth to make a complete rotation on its axis; "two days later they left"; "they put on two performances every day"; "there are 30,000 passengers per day"
The amount of time that elapses between successive passages of the Sun across the Meridian
The period of the rotation of the Earth with respect to the Sun The mean solar day is the time of the rotation with respect to the mean Sun The solar day commencing at midnight is called a civil or calendar day, but if the day is reckoned from noon it is known as an astronomical day because of its former use in astronomical calculation
The complete rotation of the earth in relation to the sun Although it varies, an average has determined a mean solar day of 24 hours It is universally used for civil purposes