Definition
AM and PM
AM and PM distinguish the two halves of a day on a 12-hour clock.
What it means
The same clock number happens twice each day. AM tells you it is in the midnight-to-noon half; PM tells you it is in the noon-to-midnight half.
Remember it
AM starts at midnight; PM starts at noon.
Example
School begins at 8:00 AM. A film begins at 8:00 PM. The clock numbers match, but the PM time is 12 hours after the AM time.
Watch for
AM and PM belong to the 12-hour clock. A 24-hour time such as 20:00 does not use either label.
Common mix-up
12 AM is midnight, and 12 PM is noon; writing midnight or noon can be clearer.
Exact meaning
On a 12-hour clock, AM labels times from midnight up to before noon, and PM labels times from noon up to before midnight.