Noun
a day reckoned from midnight to midnight
Source: WordNetCommon convention in modern times is for the civil day to begin at midnight, i.e. 00:00, and last a full 24 hours until 24:00 (i.e. 00:00 of the next day). Source: Internet
The most common convention starts the civil day at midnight : this is near the time of the lower culmination of the Sun on the central meridian of the time zone. Source: Internet
Therefore, although typically 86 400 SI seconds in duration, a civil day can be either 86 401 or 86 399 SI seconds long on such a day. Source: Internet
This difference from the civil day often leads to confusion. Source: Internet