In engineering, maintainability is the ease with which a product can be maintained to:

• correct defects or their cause,
• Repair or replace faulty or worn-out components without having to replace still working parts,
• prevent unexpected working conditions,
• maximize a product's useful life,
• maximize efficiency, reliability, and safety,
• meet new requirements,
• make future maintenance easier, or
• cope with a changing environment.

In some cases, maintainability involves a system of continuous improvement - learning from the past to improve the ability to maintain systems, or improve the reliability of systems based on maintenance experience.

In telecommunication and several other engineering fields, the term maintainability has the following meanings:

• A characteristic of design and installation, expressed as the probability that an item will be retained in or restored to a specified condition within a given period of time, when the maintenance is performed by prescribed procedures and resources.
• The ease with which maintenance of a functional unit can be performed by prescribed requirements.