The 12-hour clock is a time convention that splits the 24 hours of the day.
The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods : a.m. ( from the Latin , ante meridiem , meaning before midday ) and p.m. ( post meridiem , meaning past midday ) . The 24 hour/day cycle starts at 12 midnight ( often indicated as 12 a.m. ) , runs through 12 noon ( often indicated as 12 p.m. ) , and continues to the midnight at the end of the day .