a.m. time definition
Usage note Expand. The abbreviation a.m. for Latin ante meridiem, meaning “before noon,” refers to the period from midnight until noon. One minute before noon is 11:59 a.m. One minute after noon is 12:01 p.m. Many people distinguish between noon and midnight by saying 12 noon and 12 midnight. I think we all know that A.M. represents the “morning” hours, and P.M. represents the evening hours. I always thought of it this way: A.M. = after midnight…….P.M. = pre-midnight. 1 Terms 12 a.m. and 12 p.m. cause confusion and should not be used as neither the 12 am nor the 12 pm designation is technically correct.  It advisable to use 12 noon and 12 midnight where clarity is required. Most English speakers know that a.m. refers to the hours from midnight and noon, and p.m. to the hours from noon and midnight. The term we associate with the morning, a.m., is an abbreviation the Latin phrase ante merīdiem meaning “before midday”; p.m. is an abbreviation of post merīdiem, meaning—you guessed it—“after midday.” These two terms help keep ambiguity at bay in the 12-hour time system. In formal writing, it is best to lowercase both a.m. and p.m. and retain the periods (as opposed to writing them AM/PM or am/pm); however, should you choose to use a different format, the most important rule is to be consistent throughout your piece. Latin = after midday. after noon. 1  Terms 12 a.m. and 12 p.m. cause confusion and should not be used as neither the 12 am nor the 12 pm designation is technically correct.  It advisable to use 12 noon and 12 midnight where clarity is required. Note that when a.m. or p.m. end a sentence, as in The train is arriving at 10 p.m., it is not necessary to place an additional period at the end. And, for our final writing tip, since these abbreviations specify an hour’s relation to noon, it is not necessary to use morning, evening, night, or o’clock with them. AM* and PM* Abbreviation(s), Latin phrase, Meaning. 1  Terms 12 a.m. and 12 p.m. cause confusion and should not be used as neither the 12 am nor the 12 pm designation is technically correct.  It advisable to use 12 noon and 12 midnight where clarity is required. AM* and PM* Abbreviation(s), Latin phrase, Meaning. Terms 12 a.m. and 12 p.m. cause confusion and should not be used as neither the 12 am nor the 12 pm designation is technically correct.
It means “before noon,” refers to the period from midnight until noon.