They are latin abbreviations, ante meridiem (before midday) for a.m and post meridiem (after midday) for p.m.
antemeridian is AM; postmeridian is PM.
Go To Ask.Com
The acronym PM can mean post meridian, which is the time from noon until midnight, or it can mean prime minister.
AM: Ante Meridiem; PM: Post Meridiem
post meridem
Am = Ante meridian and Pm = post meridian
Tornadoes can form at any time of day or night. The time from 3 PM to 9 PM is the most common time for tornadoes to form.
2100
It is necessary to specify the hour when giving the time in that form.
8:22 pm
AM is ante meridian - After 12Midnight and before 12 Noon. PM is post meridian - After 12 Noon and Before 12 Midnight.
From PM today to PM tomorrow is a duration of 24 hours. This period includes the entire span of one full day. If you consider it from a specific PM time today to the same PM time tomorrow, the count remains 24 hours.