Software Testing : Differences Defect Severity Vs Priority

Defect severity and priority is one of the most basic and often ambiguous terminologies in software testing field. Below table tries to differentiate software defect severity and priority.

Defect Severity	Defect Priority
Severity equates to Impact	Priority equates to sense of urgency
Assigned by a person who opens a defect/bug e.g. SQA engineer, Support engineer, Software engineer etc.	Assigned by a person who owns and understands customer requirements and release requirements .e.g. Software Development Manager, Project Manager etc.
Categorization of defect severity for an organization is predefined. Generally integrated in defect management system	Categorization of defect priority for an organization is predefined. Generally integrated in defect management system
Defect severity categorization example… S1 – High S2 – Medium S3 – Low	Defect priority categorization example… P1 – High P2 – Medium P3 – Low
S1 examples… Crashes, core-dump,memory leak,data loss, security vulnerabilities, show-stopper ,i.e. anything that prevents product from functioning,	P1 examples… Direct customer impact, may affect release schedule if not fixed
S2 examples… Severe feature issues, occasional crashes, may not always be reproducible such as corner cases, affects major product functionality but has reasonable workaround, reasonable customer impact	P2 examples… any sever issue that should be fixed as soon as possible, may affect the further testing or development of either same or dependent feature
S3 examples… minor functionality problems, word spacing, grammatical mistakes, low customer impact	P3 examples… any bug that can be fixed in due course of development

Please note that categorization & examples of priority and severity are subjective and depends on an organization.