The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods: a.m. and p.m.. Each period consists of 12 hours numbered: 12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11. The 24-hour/day cycle starts at 12 midnight, runs through 12 noon, and continues just before midnight at the end of the day. The 12-hour clock was developed from the middle of the second millennium BC to the 16th century AD.
