Planned preventative maintenance (PPM) is maintenance carried out on a schedule before equipment fails: servicing the HVAC quarterly, testing fire alarms weekly, inspecting lifts monthly. It is the opposite of reactive maintenance, which waits for the breakdown.
PPM is cheaper than failure in almost every case that matters: an unplanned outage costs repair fees plus disruption plus, in regulated areas, compliance exposure. A PPM schedule is also the backbone of most compliance evidence.