Subscriptions in Azure API Management is a concept to say what APIs can be used by whom.
Let’s say you host an online magazine and want to monetize your APIs by having different pricing categories for your APIs.
The Free category contains the FreeNews API and is accessible for all API consumers, unregistered and registered users of APIM.
The Bronze category contains the PaidNews API which contains premium articles that an APIM user must pay for.
Silver contains several APIs that are related to creating ads on your online magazine platform; we can bundle those in an APIM product.
And finally there is a Gold category that contains all APIs.
In a nutshell, a subscription describes the relation between a user and the APIs that are accessible for this user by sending a subscription key as part of a request.