12-hour clock | Description, History, and Facts | Britannica
https://www.britannica.com/topic/12-hour-clock
Web12-hour clock, time convention that splits a 24-hour day into two equal 12-hour periods. The first is referred to as am, which stands for ante meridiem, “before midday” in Latin, while the second is referred to using pm, meaning post meridiem, or “after midday.”.
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