A "SEV" (severity) is a production failure or incident, usually indicted with a level value.

For example, a SEV 0 would be a total system unavailability incident, SEV 1 might be a major issue with parts of the system, SEV 3 is a less critical failure affecting a subset of users, etc.

You'll typically have a postmortem meeting afterwards to discuss the incident, the root cause, lessons learned, and action items to prevent future occurrences, which is the meeting described in the article.

In this context, it refers to an incident. Incidents are often referred to by their severity, such as SEV1, SEV2, etc.

E.g.

https://www.gremlin.com/community/tutorials/how-to-establish...

https://www.atlassian.com/incident-management/kpis/severity-...

https://response.pagerduty.com/before/severity_levels/

SEVerity level of the incident