mock server are backend application that mocks a real one by responding to request with pre-defined result.
They are used mainly in the development of web application in order to mock a Web service (such as rest)
A mock server is configured as a proxy gateway in the development environment.
proxy or/and sniffer can also respond
yarn global add @stoplight/prism-cli
prism mock -d https://raw.githack.com/OAI/OpenAPI-Specification/master/examples/v3.0/petstore-expanded.yaml