The full form of AM is Ante-Meridiem, which is a Latin term used to indicate a 12-hour clock system before noon. The 12-hour system splits a days time cycle into two parts, and AM or Ante Meridiem represents the first period, which is midnight to noontime. On the other hand, the full form of PM is Post Meridiem, which is another Latin term used to indicate the 12-hour clock system after noon. The system of 12-hour clocks splits the period into two equal parts, the first period and the second period, and PM or Post Meridiem reflects the second period, which is from noon till midnight. In a 12-hour clock, AM and PM are used to prevent ambiguity when referring to time. AM represents the morning, while PM represents the afternoon and evening.