Confused about AM and PM? ⏱️ Learn the difference, avoid common mistakes, and understand how 12-hour time compares to 24-hour format. Online shopping for from a great selection at All Departments Store. The 24-hour clock is a method of telling the time in which the civil day runs from midnight until next midnight. The following numbers (used once in the same civil day) of hours are: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 and 23, without AM nor PM. Originally there were two cycles: one cycle which could be tracked by the position of the Sun (day), followed by one cycle which could be tracked by the Moon and stars (night). This eventually evolved into the two 12-hour periods which are used today, one called a.m. starting at midnight and another called p.m. starting at noon. [1] AM means before noon. This is the 12-hour period from midnight to noon. PM means after noon. It covers the 12 hours from noon to midnight. Using numbers from 1 to 12, followed by am or pm, the 12-hour clock system identifies all 24 hours of the day. Discover books, yoga DVDs, and entertainment in the AM collection. Find your next read or workout today. Explore top New York news and sports with amNewYork. Get the latest city insights and headlines. Your premier NYC news source! Separate the abbreviations from their number with a non-breaking space. The abbreviations stand for ante meridiem (before noon) and post meridiem (after noon) and are used strictly with twelve-hour time. AM and PM are the abbreviated terms for Ante Meridiem and Post Meridiem respectively. While AM represents the time from midnight to 11:59 noon, and PM represents the time from 12 noon to 11:59 midnight. As we said above, AM stands for “ante meridiem” or before noon in Latin, so it is used to describe the first portion of the day – the first 12 hours. On the other hand, PM stands for “post meridiem” or after noon in Latin and it’s used to describe the second portion of the day – the final 12 hours.