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. Online shopping for from a great selection at All Departments Store. 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. Allied Mastercomputer (also called Adaptive Manipulator or Agressive Menace ), or AM, the antagonist in the short story and video game I Have No Mouth, and I Must Scream by American writer Harlan Ellison 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. Confused about AM and PM? ⏱️ Learn the difference, avoid common mistakes, and understand how 12-hour time compares to 24-hour format. 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. Find and listen to live AM radio stations from every corner of the United States. Enjoy your favorite music, shows, and news with ease. This is the Top Song Pick on our website as of Mon, Jul 27, 2026, 12:00 AM, EDT. 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].