This is an English teaching entry targeting at Chinese readers.
What does 12:00 pm mean? Most Chinese people will think that 12:00 pm means midnight and 12:00 am means noon. It is wrong.
One of my colleagues got an Email before our CEO:
Please give me a release before 12:00 pm Beijing Time.
She was still working on it at 13:00 when CEO called and asked why she had not given the release. She answered that she thought that 12:00 meant midnight.
What American Heritage Dictionary says about a.m.:
or A.M. Latin. anno mundi (in the year of the world).
also a.m. or A.M.ante meridiem.
Usage Note: By definition, 12 A.M. denotes midnight, and 12 P.M. denotes noon, but there is sufficient confusion over these uses to make it advisable to use 12 noon and 12 midnight where clarity is required.
And what Wikipedia says:
The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided, or separated into two periods called ante meridiem (a.m., from Latin, literally "before midday") and post meridiem (p.m., "after midday"). Each period consists of 12 hours numbered 12 (acting as a zero), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. The a.m. period runs from midnight to noon, while the p.m. period runs from noon to midnight. The most common convention is to assign 12 a.m. to midnight and 12 p.m. to noon, defining both half days to have a closed (inclusive) beginning and open (exclusive) end. 12 noon and 12 midnight can more clearly and correctly express these times.
Therefore, generally speaking, 12:00 pm denotes noon and 12:00 am denotes midnight. Using 12 noon and 12 midnight is suggested as it can avoid understanding.