What does “AM” and “PM” stand for?

“AM” stands for “ante meridiem” which is Latin for “before midday” and refers to the period of time between 12:00 midnight and 11:59 in the morning. “PM” stands for “post meridiem” which is Latin for “after midday” and refers to the period of time between 12:00 noon and 11:59 at night. These terms are used to differentiate between the morning and afternoon/evening hours of the day in the 12-hour clock system. The 24-hour clock system, used in many countries around the world, does not use “AM” and “PM” but instead expresses time using numbers from 0 to 23.