We use the terms a.m. and p.m. many times a day when referring to the time. Do you know what they actually stand for, and how they came about?
a.m. comes from the Latin words 'ante meridiem' meaning before midday.
This covers the hours from 12a.m. to 11.59a.m.
We then reach noon and the p.m. is used until midnight.
p.m. comes from the Latin words 'post meridiem' meaning past midday.
This covers the hours from 12p.m. to 11.59p.m.
The day was divided into two cycles. One that was tracked by the sun and the other by the moon. The 12 hour clock is not as common as you might think. It is just because its used in countries we know well, like New Zealand, Australia, United Kingdom, United States, India and a few others. The 24 clock is actually the more widely used way of telling the time, so it is still very important to be able to read the time this way.
The 12 hour clock has been traced as far back as the ancient Egyptians around 1500BC, so it sure is a proven method for telling time.