The What, Why, and How

What Is Software Quality?

In Webster's dictionary, quality is defined as: "The essential character of something, an inherent or distinguishing character, degree, or grade of excellence." Software quality must be defined in terms that are meaningful to the software's users. What is most important to them, and what do they need?
Software quality is commonly described in terms that are known as quality attributes. A quality attribute is a property of a software product that will be judged directly by stakeholders. Quality attributes are—and should be—quantifiable in specifications by appropriate and practical scales of measure. The ISO software-quality model  defines six quality-attribute categories: functionality, reliability, usability, efficiency, maintainability, and portability. The categories, in turn, are further subdivided into subcharacteristics.

To be useful, software-quality attributes need not only be defined, but also confirmed and enforced. The IEEE [IEEE 1997] defines a software-quality audit as:

An independent examination of a software product, software process, or set of software processes to assess compliance with specifications, standards, contractual agreements, or other criteria. It provides an independent evaluation regarding conformance of software products and processes to applicable regulations, standards, guidelines, plans, and procedures.