what does am and pm stand for

AM stands for "ante meridiem," which is Latin for "before midday." It refers to the time from midnight to just before noon (12:00 a.m. to 11:59 a.m.). PM stands for "post meridiem," which means "after midday." It refers to the time from noon to just before midnight (12:00 p.m. to 11:59 p.m.). These terms are used in the 12-hour clock system to differentiate the first half of the day (AM) from the second half of the day (PM). Noon is referred to as 12:00 PM, while midnight is 12:00 AM. The system has been in use since ancient times and helps indicate whether the time is in the morning or afternoon/evening.