Which Latin phrase represents the abbreviation P.M.?

The phrase that represents the abbreviation P.M. is "Post meridiem," which translates to "after midday" in English. This term is used to indicate the time from noon until midnight in the 12-hour clock system. Understanding this phrase can help clarify the distinction between morning hours, which are marked as A.M. (ante meridiem, meaning "before midday"), and evening hours, which are represented by P.M.

In contrast to this, the other phrases listed do not match the abbreviation's meaning. "Plus meridiem" does not exist in Latin and therefore lacks proper context. "Praeter meridiem" and "Pro meridiem" also do not convey the intended meaning of being after noon. Therefore, the choice "Post meridiem" is the correct one for representing P.M.