Software quality describes how well a program meets its stated requirements and the real needs of the people who use it. The IEEE Computer Society’s Guide to the Software Engineering Body of Knowledge (SWEBOK) treats Software Quality as one of its core knowledge areas, alongside design, testing, and maintenance, reflecting how central the concept is to the discipline.
It is useful to split quality into two families. External qualities are visible to users and operators: correctness, reliability, usability, performance, and security. Internal qualities are visible mainly to developers: maintainability, readability, and the ease with which the code can be changed without breaking. Both matter, because software that works today but cannot be safely modified tomorrow has hidden costs.
Quality is not a single check at the end of a project. It is the target that testing, code reviews, and good design all aim at. SWEBOK frames quality as something planned for and managed throughout development, with techniques for measuring it and processes for assuring it, rather than a property that can be inspected in after the fact.
Because “quality” means different things to different stakeholders, teams usually make it concrete by naming the specific attributes they care about and how they will be measured. That turns a vague goal into something a team can actually verify and improve.