O'clock: used when the time is exactly on the hour (e.g., 3:00 is "three o'clock").
Quarter past: 15 minutes past the hour (e.g., 2:15 is "quarter past two").
Half past: 30 minutes past the hour (e.g., 4:30 is "half past four").
Quarter to: 15 minutes before the hour (e.g., 5:45 is "quarter to six").
AM/PM: used to indicate morning (AM) or afternoon/evening (PM).
Midnight and noon: specific times used in the 12-hour format.