Defect severity and priority

• Priority of a bug is the urgency of need to fix the bug.
• Severity of a bug is the impact it has on the system. 

Severity
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S1 - Critical: Defect affects critical functionality / data. No workaround.
S2 - Major: Defect affects major functionality / data. Has workaround, but is difficult / complicated.
S3 - Minor: Defect affects minor functionality / non critical.
S4- Low: Does not affect functionality or data. No need for a workaround.
S5 - Cosmetic: Defect affects only the look & feed, but not the functionality.

Priority
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P1 -- High: Defect must be fixed ASAP.
P2 -- Medium: Defect can wait until the next build / release.
P3 -- Low: Defect can be deferred until a more serious defect is fixed.