Pure-reference catalog for defect classification: severity (impact on the system / user) vs priority (urgency of fix) on independent axes - the canonical 5-point severity scale (Critical / High / Medium / Low / Trivial), the 5-point priority scale (Immediate / High / Medium / Low / Deferred), the 5x5 matrix with worked S1/P5 and S5/P1 examples, and IEEE 1044-2009 severity classes; plus the full defect lifecycle (ISTQB-canonical states new / open / assigned / fixed / verified / closed / reopened / deferred / rejected / duplicate, allowed and forbidden transitions, tracker vocabulary maps) and the defect-categorisation taxonomies (IEEE 1044 anomaly classification, ISTQB CTAL-TA root-cause categories, Orthogonal Defect Classification) in references. Use when triaging or classifying a defect, configuring a tracker's severity/priority/state fields, reviewing a bug report's classification, or running root-cause analysis.