OxScience

The Basic Difference between am and pm is that The term AM or ante meridiem is a term used to define the hours after midnight and before noon. The term PM defines the hours afternoon and before midnight.

A.M

am is the abbreviation for the Latin term Ante meridiem which literally means before noon.

This term is a Latinism and an adverbial phrase. Refers to hours after midnight or 00:00 hours and before noon or 12:00 hours. It is important to emphasize that it should be abbreviated to AM and not AM.

12-hour clocks were created in the middle of the second millennium. Over the course of the last 4000 years, the watch underwent a series of transformations and it was not until the 16th century that it took on the appearance we know today.

Each day began at midnight and this time was known as 00:00 on clocks with a 24-hour format. For clocks that have a 12-hour format, the day begins at 12 am and the second 12-hour cycle begins at 12 pm or 12 noon.

In ancient times, the first 12 hours were taken into account only during the day and the remaining 12 hours, when night fell.

p.m

It is short for Post meridiem, the Latin term meaning “afternoon.” It is a Latinism and an adverbial phrase that refers to the hours afternoon and before midnight.

This term should be abbreviated as pm and not PM.

Differences between am and pm

• am is used as an abbreviation for “ante meridiem.”
• pm is used as an abbreviation for “post meridiem”.
• am refers to the hours between 00:00 and 12 noon.
• pm refers to the hours between 12 noon and 00:00 hours.
• Both terms are used in countries that operate the 12-hour system and not the 24-hour system or military system.