A notified body is an independent, third party, accredited body which is entitled by an authorized accrediting body. Upon definition of standards and regulations, the accrediting body may allow a notified body to provide verification and certification services. These services are meant to ensure and assess compliance to the previously defined standards and regulations, but also to provide an official certification mark or a declaration of conformity.
In the European Union a notified body is an entity that has been accredited by a Member State to assess whether a product to be placed on the market meets certain preordained standards. Conformity assessment can include inspection and examination of a product, its design, and the manufacturing environment and processes associated with it. For example, a notified body may designate that a medical device conforms to the E.U. Medical Devices Directive, which defines the standards for medical devices. With this Declaration of Conformity, the manufacturer can label the product with the CE Mark, which is required for distribution and sale in the E.U. Additionally, the E.U. member state accrediting the notified body will then inform the European Commission that the product complies with set standards (or not).
Find here a list of MDR-certified notified bodies