"Those activities involving continuous or periodic monitoring and diagnosis in order to forecast component degradations so that as-needed, planned maintenance can be performed prior to equipment failure."

• Monitoring means watching carefully
• Diagnosis means to determine health status
• Forecast means to project or predict future status
• Degradations means deficiencies (relative to best possible health)
• Maintenance in the context of the definition means to return the health to normal
• Prior to failure means before complete loss of function or incapacitation

So the philosophy of Predictive Maintenance is to: Watch carefully, determine health status (on a continuous or periodic basis), predict future status based on deficiencies found and return health to normal before complete loss of function.

Tip provided by Jack Nicholas Jr., Author, The Predictive Maintenance Management Book