Some say it's “after midnight” or “past midday,” but that isn't exactly true... In fact, like many words and phrases in the English language, a.m. is short for a Latin phrase, “ante meridiem” (or “before midday”), while p.m. is short for “post meridiem” (or “after midday”).
AM = Ante meridiem: Before noon
PM = Post meridiem: After noon
When we talk about time in day or night, we use pm or am. Many has no idea what exactly does this mean. That is exactly we have listed what does am and pm stands for and how to use this in normal conversations.
You can say, "I will reach there by 1 pm". This means you will reach the destination on afternoon. The afternoon part is evident when you say pm after time.
You can also say "John will come by 10 am". This mean John will reach here in the morning.