severity (n)~ The property of an alert indicating its seriousness. Examples include Service Unavailable Security Issue Critical Error Error Warning Information and Success. severity (n)~ In ACT the importance your organization attaches to a particular update. severity (n)~ In Server Manager and Event Viewer the urgency of an event or error condition system fault failure or action by either the system or the user. Severity can be any of four industry-standard values: Information Warning Error or Critical. These values are defined in the Event Viewer Help.