- or pmabbreviation for the Latin post meridiem, "after noon," used after a time to indicate that the time occurs after 12:00 noon. Thus 4:30 pm is the same as 16:30. The notations "AM" and "PM" are used extensively in English speaking countries and especially in the United States, where time is usually not stated on a 24-hour basis. Note: By convention, midnight is represented as 12:00 am and noon as 12:00 pm. In text, however, it is best to avoid the use of 12:00 am or 12:00 pm since the reader may not be aware of these conventions.
Dictionary of units of measurement. 2015.