A.M. stands for "Ante Meridiem," a Latin term meaning "before midday." It is used to designate the time from midnight (12:00 AM) to just before noon (11:59 AM). This system helps differentiate between morning and afternoon hours in the 12-hour clock format. In contrast, the term P.M. (Post Meridiem) refers to the time from noon to midnight. The use of A.M. and P.M. is common in many countries, particularly in the United States, to avoid confusion in scheduling events, appointments, and daily activities.