The Increment is the sum of all the Product Backlog items completed during a Sprint and the value of the increments of all previous Sprints. At the end of a Sprint, the new Increment must be “Done,” which means it must be in usable condition and meet the Scrum Team’s definition of “Done.” It must be in usable condition regardless of whether the Product Owner decides to actually release it.
The Scrum Guide is the official Scrum Body of Knowledge. It was written by Ken Schwaber and Jeff Sutherland, co-creators of Scrum. To access the full guide please visit it scrumguides.org