It is classified into two, which are:
Prevention Maintenance:
This is maintenance carried out at predetermined intervals, or other prescribed criteria, and intended to reduce the likelihood of an item not meeting an acceptable diagnostic test, lubricating, adjusting and cleaning.
Corrective Maintenance
It is a maintenance carried out to restore an item which has ceased to meet an acceptable rendition. This involves troubleshooting to detect the cause of any fault and then either repaired or replaced.