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

a.m.

also am us uk /ˌeɪˈem/
The bell rang at 8 a.m., regular as clockwork.The shop is open daily from 8 a.m. to 6 p.m.The 7 a.m. team arrived to relieve the night workers.Opening hours: 9 a.m. - 6 p.m.We should land in Madrid at 7 a.m.

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)