AM and PM Explained
How does the 12-hour clock system work? Is midnight 12 am or 12 pm?
Elsewhere on timeanddate.com
Daylight Saving Time (DST)
Why do many countries set the clocks back and forth an hour twice a year?
About the 12 Months
Why are there 12 months? How long are they, and what do the month names mean?
UTC: Coordinated Universal Time
Coordinated Universal Time (UTC) is the basis for civil time today. This 24-hour time standard is kept using highly precise atomic clocks combined with the Earth's rotation.