ante meridiem
time period
Also known as: AM, a.m.
Quick Summary
Ante meridiem, abbreviated as AM, is a Latin phrase meaning "before noon." It designates the time period from midnight to noon in the 12-hour clock system. This system divides the 24-hour day into two 12-hour segments, with AM representing the first half and PM (post meridiem, meaning "after noon") representing the second half. The use of 12-hour periods has historical roots in ancient civilizations like the Babylonians and Egyptians, who divided time based on lunar patterns and celestial observations.123
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