Which of the following is NOT a time-box in Scrum?

A key aspect of Scrum is the use of time-boxes, which are fixed periods during which specific activities and processes are carried out. Each official event within a Sprint, including Sprint Planning, Sprint Review, and Sprint Retrospective, has a defined time-box that ensures the team remains focused and delivers value effectively.

The concept of "Sprint 0" is not a recognized time-box within the Scrum framework. Instead, it often refers to the preparatory stage or activities before the first official Sprint, which can include things like team formation, backlog creation, and setting up the working environment. However, it does not have an official status or time-box assigned to it in Scrum practices, as it falls outside the well-defined events that occur during a Sprint.

In contrast, the other options are all established time-boxes vital to the Scrum process. Sprint Planning specifies the time allocated for the team to plan the work for the sprint, the Sprint Review is the time-boxed meeting to inspect what was delivered during the Sprint, and the Sprint Retrospective focuses on reflecting and improving team processes.