Meaning of “a.m.” - Learner’s Dictionary

a.m.

( also am) uk us /ˌeɪˈem/

A1 used to refer to a time between 12 o'clock in the night and 12 o'clock in the day:

We're open from 9 a.m. to 5 p.m. daily.

(Definition of “a.m.” from the Cambridge Learner’s Dictionary © Cambridge University Press)