12hour

The 12-hour clock is a timekeeping convention that divides the 24-hour day into two cycles of 12 hours. Each cycle is labeled with AM (ante meridiem) for hours from midnight to noon and PM (post meridiem) from noon to midnight. In this system, hours are typically written from 1 to 12, with 12 marking the transition points at midnight and at noon. For example, 12:01 AM is just after midnight, while 12:01 PM is just after noon.

History and context: The 12-hour division has ancient antecedents and was further formalized in medieval Europe with the spread of mechanical clocks. The abbreviations AM and PM derive from Latin terms ante meridiem and post meridiem. The 12-hour clock remains common in daily life in many English-speaking countries, even as the 24-hour clock is used in many formal contexts and in many parts of the world to avoid ambiguity.

Usage and formats: Today, many devices support both 12-hour and 24-hour formats. The 12-hour format is prevalent in spoken language and consumer electronics, where times are typically shown with an AM or PM indicator. Some contexts prefer explicit labeling or the words noon and midnight to reduce confusion at 12:00. In formal settings, the 24-hour clock is often favored for clarity in timetables and schedules.

See also: 24-hour clock; time notation; ISO 8601. The concatenated form 12hour is sometimes used in programming or product naming to indicate a 12-hour time format, but the standard term is the 12-hour clock.