AM and PM: What Do They Mean? - timeanddate.com
https://www.timeanddate.com/time/am-and-pm.html
WEBAM = Ante meridiem: Before noon; PM = Post meridiem: After noon; Using numbers from 1 to 12, followed by am or pm, the 12-hour clock system identifies all 24 hours of the day. For example, 5 am is early in the morning, and 5 pm is late in the afternoon; 1 am is one hour after midnight, while 11 pm is one hour before midnight.
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