"What does A.M. and P.M. stand for?"

Last night my nine year old asked her daddy what does a.m. and p.m. stand for? I wasn't sure so I had to google it. This is what we told her;

A.M. means:

Origin: L ante meridiem
before noon: used to designate the time from midnight to noon, also A.M., a.m., or am
 
P.M. means:
 

P.M. also p.m. or P.M.

abbreviation post meridiemUsage Note: By definition, 12 A.M. denotes midnight, and 12 P.M. denotes noon, but there is sufficient confusion over the meanings of A.M. and P.M. when the hour is 12 to make it advisable to use 12 noon and 12 midnight where clarity is required.
 
Taken from; http://www.yourdictionary.com/p-m-abbv