The granting of the ability (1) to a specific user, (2) to perform a specific action, (3) on a specific content object.
Permissions are usually granted in aggregate. For example, the Editors group has all permissions over all content. Or, Alice has publish permission on all content in the News section. Additionally, permissions on objects are often inherited from a parent object or folder, rather than being assigned directly.
The technical name for a single permission is an Access Control Entry which are then aggregated into access control lists. The effect of permissions in aggregate is known as the discipline of subsystem of authorization.