SharePoint Sandboxed soultion is a new feature in SharePoint 2010.
SharePoint 2010 provides a new sandboxed environment that enables us to run user solutions without affecting the rest of the SharePoint farm. This environment means that users can upload their own custom solutions without requiring intervention from administrators, and without putting the rest of the farm at risk. This means that the existing sites\pages or components will not be effected by the newly added solution.