Software Quality
Software quality is how well a product meets both its explicit requirements and the implicit expectations users bring to it — correctness, reliability, performance, usability, and security among them. It's not a single measurable number; it's a combination of dimensions that trade off against each other depending on what the product actually needs to be good at.
The ISO 25010 standard breaks software quality into eight characteristics — functional suitability, performance efficiency, compatibility, usability, reliability, security, maintainability, and portability — as a way to make an otherwise fuzzy concept concrete enough to actually evaluate against. No product excels at all eight; a real-time trading system prioritizes performance and reliability over portability, a marketing site prioritizes usability over raw performance.
Software quality is the outcome QA exists to influence — testing, process, and standards are all means to that end, not the end itself. This is worth remembering when a team optimizes hard for one dimension (test coverage numbers, say) without checking whether it's actually moving the needle on quality the user experiences.
