Reseller-specific privileges (the ones that do not affect service subscriptions that resellers create for their customers) are as follows:
Ability to use remote API
Defines if a reseller can remotely manage websites through custom applications. The remote API is an interface that can be used for developing custom applications integrated with websites, which could be used, for instance, for automating setup of hosting accounts and provisioning of services for customers purchasing hosting services from your site. To learn more, refer to the Plesk API documentation.
Access to Plesk
Defines if a reseller can use the Plesk graphical user interface.
Customer account creation
Defines if a reseller can create user accounts and subscriptions for their customers in Plesk.
Defines if a reseller can set up overselling policy, meaning that a reseller can themselves define if overselling is allowed to them or not.
Meanings of the other permissions are the same as in hosting plans and subscriptions.