What is an Impediment (Blocker)?
An impediment is anything slowing or stopping the team's progress: a blocked dependency, a missing decision, a broken environment, an organizational policy. Surfacing them fast is a core standup purpose; removing them is the scrum master's signature duty — especially the ones above the team's own authority.
The maturity marker is how impediments age: healthy teams measure blocker resolution in hours or days and keep a visible impediment board; unhealthy ones normalize waiting until it's just "how things are here."
Worked example
Standup, day 4: "still waiting on security sign-off for the API scopes — six days now." The scrum master walks it up the same morning, discovers the reviewer left the company and the queue was orphaned, and has a new reviewer assigned by lunch. The impediment wasn't the review; it was that nobody with reach had been told the queue led nowhere.