Defect
// Definition
A flaw in a software system that causes it to behave in an unintended or incorrect way — also called a bug or fault. A defect arises when actual behaviour diverges from expected behaviour defined by requirements or specification. In QA workflow, a defect is formally logged with reproduction steps, severity, and priority, then tracked through the bug lifecycle from discovery to verified closure. The distinction that matters in practice: an error is the human mistake, a fault is the resulting code flaw, and a failure is the observable incorrect behaviour at runtime.
// Related terms
Bug Lifecycle
The stages a defect passes through from discovery to closure: New → Assigned → In Progress → Fixed → Verified → Closed (with possible Reopened, Deferred, or Rejected branches).
Severity
A rating of how badly a defect affects the system or users, independent of when it should be fixed. Common levels: critical (system unusable or data loss), major (core feature broken with no workaround), minor (non-critical degradation), trivial (cosmetic only). Severity measures impact; priority measures urgency — a cosmetic bug on the login page might be low severity but high priority for a public launch.
Priority
A classification of how urgently a defect must be fixed, set by product management based on business impact, release schedule, and customer commitment. Priority answers 'when should this be fixed?' — a cosmetic defect on a high-traffic page may be P1 urgency despite low severity, while a rare data-loss bug may be deferred to a future release (P3) despite high severity. Priority drives sprint planning; severity drives technical risk assessment. The two dimensions are deliberately independent to give product and engineering separate levers.
Reproduction Steps
A numbered sequence of actions a developer can follow to reliably trigger a defect from a known starting state. High-quality reproduction steps include: the environment and version, preconditions and test data, each action in order, and the actual vs expected result. Reproducibility is the single biggest factor in defect resolution speed — a bug that cannot be reproduced is rarely fixed. For intermittent defects, include the reproduction rate and any environmental conditions that affect it.