The Sprint Goal is defined by the Scrum Team during Sprint Planning. It is a concise articulation of the single objective for the Sprint.
The Sprint Goal gives the Scrum Team a clear goal for the Sprint. It provides clarity and focus to the Scrum team. Having a shared goal also helps promote collaboration and teamwork where all the members of the Scrum team are working towards a common goal rather than working on separate initiatives.
The Sprint Goal also provides the Scrum team a clear focus whilst also allowing for autonomy and flexibility in determining exactly how they will achieve it. This allows the actual work within the Sprint to be adaptive and flexible.
As the Sprint progresses, the Scrum team keeps the Sprint Goal in mind. Each day during the Daily Scrum the Scrum team inspect their progress towards the Sprint Goal and adapt their Sprint Backlog where necessary to ensure they are still meeting their Sprint Goal.