Maintenance includes all measures that are part of maintaining or restoring the usable condition of a property. These measures can be divided into four categories: Inspection, maintenance, repair and improvement.
Maintenance includes all operations that involve maintaining the functionality of equipment (e.g. a heating engineer replacing the rubber seal on the heater every year).
Repairs of all kinds are subsumed under the term repair.
In contrast, improvement means that after a repair the end result is better than the initial condition before the defect, e.g. a component is replaced by a newer and better performing part.