APIs represent real backend APIs (Application Programming Interfaces). An API is also known as a service, which offers a HTTP, REST or SOAP interface that can be invoked remotely by a client.
Scheer PAS API Management provides a way to turn unmanaged (raw) back-end APIs into managed APIs by attaching policies to them. Any policies configured on an API will be applied at runtime, regardless of the client and API contract.
An API has to be fully configured, including policies and implementation (and in case of public APIs including plans) to be published. If the API has been published to the gateway it can be consumed - in case of private APIs by clients.
Refer to API Management Guide > APIs for more details.