Is noon AM or PM?

Neither noon nor midnight are either AM or PM. "AM" stands for the latin phrase "ante meridium" and "PM" stands for "post meridium", where "meridium" means noon. Noon is neither before nor after noon; it is noon. In some localized areas, people use 12:00 pm to refer to noon, and in others 12:00 pm is understood to be midnight. It is advisable not to use either AM or PM for noon or midnight, but instead write out "noon" or "midnight". If you must use an abbreviation instead, there are several options (each used by various people). One popular set is "M" (for "meridies") for noon and "MN" (for "media nox") for midnight, e.g. 12:00 m or 12:00 mn. Also, the abbreviation for ante meridium is properly written several ways: "AM", "am", "A.M.", "a.m."; and correspondingly for post meridium.