Critical   

Complete loss of service or production down situations where no workaround exists.
Incidents which have a critical impact on the business’s ability to maintain operations and demand an immediate response.
The production down incident affects multiple locations or high number of users in one location.

High   

Severe loss of functionality or performance.
Major feature/product failure, where short-term workaround may be available; operation can continue in a restricted fashion. The application is usable but severely limited. Risk of impacting the deadline.
A high number of users unable to perform their functions.

Medium   

Incidents that cause non-critical product features to malfunction consistently.
Major feature/product failure where an acceptable workaround is available.
Problems with a business function in the software, which causes severe inconvenience to users.

Low  

Incidents that do not compromise production or for which a suitable workaround has been identified.
Operational questions, informational requests.
Limited impact and urgency work progress not directly impacted.