The 12-hour clock is a timekeeping convention in which the 24 hours of the ay are divided into two periods called ante meridiem (a.m., Latin "before noon") and post meridiem (p.m., "after noon"). Each period consists of 12 hours numbered 12 (acting as zero), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11. The indication of noon and midnight in the 12-hour system is disputed.