1. In general: The degree to which a set of inherent characteristics of an item fulfills ↑requirements.
2. In systems and software engineering: The degree to which a ↑system satisfies stated and implied needs of its ↑stakeholders.
Quality in this definition means fitness for intended use, as stated in the ↑requirements. This is in contrast to the colloquial notion of quality which is typically connoted with goodness or excellence.