A service account is an account that can be used by your program to perform actions in Yandex Cloud. A service account can manage other resources via the API.
The service account is a resource: just like a virtual machine, a service account is created inside a folder. You can grant or revoke access rights to the service account for other users.
At the moment, service accounts are used to access resources of the Yandex Object Storage service. For more information, see the section How to use the API in the Object Storage documentation.