Processor / data processor
A processor is a kind of contractor which takes on the data processing on behalf of a controller. This can be a natural or legal person, a public authority or another institution. For consumers, some examples for processors include payroll accounting and newsletters: The controller for the payroll is the employer, but a tax office functions as the processor. The newsletter for, say, a clothing company (the controller) is prepared and sent out by a marketing agency (the processor). Working as a data processor is legal under the General Data Protection Regulation, especially to ensure the data exchange within corporations.
Article 4(8) GDPR (Definitions)
“processor” means a natural or legal person, public authority, agency or other body which processes personal data on behalf of the controller
Source: Regulation (EU) 2016/679 (see also recitals 63 and 64)