What is the term for a timekeeping convention in which the day runs from midnight to midnight?

The correct term for a timekeeping convention in which the day runs from midnight to midnight is civil time. Civil time refers to the system of time used for everyday activities and communication among civilians, typically starting at midnight and ending at the following midnight. This system is standardized, allowing for the general public to coordinate activities, such as scheduling appointments, attending events, and conducting business.

Military time, on the other hand, typically uses a 24-hour clock for precision and avoids ambiguity in timekeeping, but it does not change the fundamental concept of the day running from midnight to midnight. Standard time is a broader term that can refer to the time used in a particular region, often based on time zones, but like military time, it doesn't specifically denote the midnight to midnight cycle. Daylight time refers to the practice of setting the clock forward during warmer months to extend evening daylight, rather than defining the structure of a day itself.