PM may refer to any of the following:
1. In chat PM is short for Private Message or Personal Message and is a message only sent between you and one other user.
2. PM is an abbreviation for power management.
3. When referring to time, pm or p.m. is short for post meridiem or past midday is the time designated after 11:59 AM noon and before 12:00 AM midnight.
5. When referring to maintenance, PM is short for Preventive Maintenance.
7. When referring to fiber-optic, PM is short for Polarization Maintaining and is also known as PMF or Polarization Maintaining Fiber. PM or PMF is an optical fiber that maintains a fixed polarization ot help increase the bandwidth and distance of how far the signal can travel.