Table 2.

Definitions of key terms used in this paper.

Term	Definition
Durability	Ability to function as required, under defined conditions of use, maintenance and repair, until a limiting state is reached
Functional lifetime	Time a product is used until the requirements of the user are no longer met, due to the economics of operation, maintenance and repair or obsolescence
Limiting event	Occurrence, which results in a primary or secondary function no longer being delivered
Limiting state	Condition after one or more limiting event(s)
Reliability	Probability that a product functions as required under given conditions, including maintenance, for a given duration without limiting event
Repair	Process of returning a faulty product to a condition where it can fulfil its intended use
Reuse	Process by which a product or its parts, having reached the end of their first use, are used for the same purpose for which they were conceived
Technical lifetime	Time span or number of usage cycles for which a product is considered to function as required, under defined conditions of use, until a failure occurs
Technical withstand (or resistance)	Capability to withstand stresses such as, for example, electrical, mechanical and environmental stresses
Upgrade	Process of enhancing the functionality, performance, capacity or aesthetic of a product