معنى (AM/PM)

“AM” stands for the Latin phrase Ante Meridiem —which
means “before noon”—and “PM” stands for Post Meridiem : “after noon.”
Although digital clocks routinely label noon “12:00 PM” you should avoid
this expression not only because it is incorrect, but because many
people will imagine you are talking about midnight instead. The same
goes for “12:00 AM.” Just say or write “noon” or “midnight” when you
mean those precise times.

It is now rare to see periods placed after these abbreviations: “A.M.” ,
but in formal writing it is still preferable to capitalize them, though
the lower-case “am” and “pm” are now so popular they are not likely to
get you into trouble.

Occasionally computer programs encourage you to write “AM” and “PM”
without a space before them, but others will misread your data if you
omit the space. The nonstandard habit of omitting the space is spreading
rapidly, and should be avoided in formal writing.