In the API Gateway service, a back end is the means by which a gateway routes requests to the back-end services that implement APIs. If you add a private endpoint back end to an API gateway, you give the API gateway access to the VCN associated with that private endpoint.
You can also grant an API gateway access to other Oracle Cloud Infrastructure services as back ends. For example, you could grant an API gateway access to Oracle Functions, so you can create and deploy an API that is backed by a serverless function.
API Gateway service to create an API gateway, you can create an API deployment to access HTTP and HTTPS URLs.
https://docs.cloud.oracle.com/en-us/iaas/Content/APIGateway/Tasks/apigatewayusinghttpbackend.htm API Gateway service to create an API gateway, you can create an API deployment that invokes serverless functions defined in Oracle Functions.
https://docs.cloud.oracle.com/en-us/iaas/Content/APIGateway/Tasks/apigatewayusingfunctionsbackend.htm API Gateway service, you can define a path to a stock response back end
https://docs.cloud.oracle.com/en-us/iaas/Content/APIGateway/Tasks/apigatewayaddingstockresponses.htm