"Post meridiem," often abbreviated as "PM," refers to the time period from noon to midnight in the 12-hour clock system. The term comes from Latin, meaning "after midday." It is used to distinguish the hours after 12:00 PM, which includes times like 1:00 PM, 2:00 PM, and so on, up to 11:59 PM. In contrast, the time period before noon is called "ante meridiem," or "AM." Both terms are essential for understanding time in many cultures, especially in countries that use the 12-hour clock format, such as the United States and the United Kingdom.