According to the Scrum Guide1, the definition of “Done” is a formal description of the state of the Increment when it meets the quality measures required for the product. The definition guides the Development Team in creating a “Done” Increment. The definition of “Done” is created by the development organization (or Development Team if none is available from the development organization). The definition of “Done” may vary significantly per Scrum Team, depending on the context. One aspect of Scrum Teams inspecting how they work toward their Product Goal is that they improve their definition of “Done” over time. Therefore, one reason why the Product Owner wants the Development Team to adhere to its definition of “Done” is to have complete transparency into what has been done at the end of each Sprint.

References: Scrum Guide