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What do a.m. and p.m. stand for when talking about time?

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closed as off topic by Jeff Atwood Apr 12 '11 at 7:03

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I think this is easily answered by resources such as wikipedia. –  JYelton Apr 5 '11 at 21:35
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1 Answer

up vote 11 down vote accepted

They are from the Latin for ante meridiem and post meridiem, which mean "before noon" and after noon", respectively.

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It is worth mentioning the crazy gotcha involving 12am and 12pm. 12pm means noon and 12:30pm is the half hour after noon. 12am means midnight. Many, many, many people get this incorrect. –  MrHen Apr 5 '11 at 20:36
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@MrHen; The confusion is usually caused by the fact that 11am is directly followed by 12pm, or 12pm is directly followed by 1pm, rather than that 12:30pm follows 12:00pm. But otherwise you're correct, it's a common mistake. :) –  falstro Apr 5 '11 at 20:56
    
@all: Probably flirting with off-topicism here (I only got here from a link on Discussion re trivial questions), but I think MrHen's point could well be useful to a number of future 'seekers after knowledge' who might not have realised they were in danger of getting it wrong, and therefore might not have actively sought the additional info. In short, I don't see why OP should be rejected as 'trivial'. –  FumbleFingers Apr 5 '11 at 23:41
    
Trying deperately to stay on-topic, I'll just say the standard rule is Midnight belongs to the new day, and woe betide any programmers, schedulers, etc. who get that wrong (but a surprising number do). –  FumbleFingers Apr 5 '11 at 23:44
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If you're worried about confusion, you can just say 12 noon or 12 midnight. –  Peter Shor Apr 6 '11 at 3:30
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