Maintainability represents the degree of effectiveness and efficiency with which a product or system can be modified by the intended maintainers (ISO 25010). Maintainability incorporates such concepts as changeability, modularity, understandability, testability, and reusability. Maintainability is responding rapidly to market conditions and keeping IT costs under control. The Maintainability of an application is a combination of compliance with good coding practices, the homogeneity with which coding rules are applied across an application, and compliance with architectural rules.
Source: IETF - The OAuth 2.0 Authorization Framework - October 2012