ISO/IEC 17020:2012 specifies requirements for the competence of bodies performing inspection and for the impartiality and consistency of their inspection activities. It applies to inspection bodies of type A, B or C, as defined in ISO/IEC 17020:2012, and it applies to any stage of inspection.
(Reference : https://www.iso.org/obp/ui/#iso:std:iso-iec:17020:ed-2:v1:en) 
The categorization of inspection bodies as type A, B or C is essentially a measure of their independence. Demonstrable independence of an inspection body can strengthen the confidence of the inspection body's clients with respect to the body's ability to carry out inspection work with impartiality.

ISO/IEC 17021-1:2015 contains principles and requirements for the competence, consistency and impartiality of bodies providing audit and certification of all types of management systems. Certification bodies operating to ISO/IEC 17021-1:2015 do not need to offer all types of management system certification. Certification of management systems is a third-party conformity assessment activity and bodies performing this activity are therefore third-party conformity assessment bodies. 
(Reference : https://www.iso.org/obp/ui/#iso:std:iso-iec:17021:-1:ed-1:v1:en)

ISO/IEC 17024:2012 contains principles and requirements for a body certifying persons against specific requirements, and includes the development and maintenance of a certification scheme for persons. 
(Reference : https://www.iso.org/obp/ui/#iso:std:iso-iec:17024:ed-2:v1:en)

ISO/IEC 17025 enables laboratories to demonstrate that they operate competently and generate valid results, thereby promoting confidence in their work both nationally and around the world. It also helps facilitate cooperation between laboratories and other bodies by generating wider acceptance of results between countries. Test reports and certificates can be accepted from one country to another without the need for further testing, which, in turn, improves international trade.

The overall aim of certifying products, processes or services is to give confidence to all interested parties that a product, process or service fulfils specified requirements. The value of certification is the degree of confidence and trust that is established by an impartial and competent demonstration of fulfilment of specified requirements by a third party.
(Reference : https://www.iso.org/obp/ui/#iso:std:iso-iec:17065:ed-1:v1:en)

ISO 15189:2012 specifies requirements for quality and competence in medical laboratories. It can be used by medical laboratories in developing their quality management systems and assessing their own competence. It can also be used for confirming or recognizing the competence of medical laboratories by laboratory customers, regulating authorities and accreditation bodies.
(Reference : https://www.iso.org/obp/ui/#iso:std:iso:15189:ed-3:v2:en)