Blocker
Also called: Showstopper
A bug so serious that it stops testing or a release from continuing.
Definition
A blocker is the highest severity level: the bug prevents a key feature from working or blocks further testing, and there is no workaround. Blockers usually must be fixed before anything is released.
In practice
Nobody can log in on the new build, so none of the other features can be tested at all.
Learn it in context
Lessons that use this term.