What is am/pm?

AM — this is the time with 00:00 before 12:00 (00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00)

PM — this is the time with 12:00 before 00:00 (12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 00:00)