The society of users in thick-server applications route their actions through the server. When they message each other, they are updating entries in the server’s database. When they publish files, they are writing those files to the server’s disks. The server has ultimate authority over those systems. Users can access the interfaces provided by the server to control them, but the server may override a user’s choice at any time. All authority is borrowed from the server, and so the users possess no authority of their own. As a result we must describe these services as authoritarian.
In thin client/thick server models, the server does all the work and has all the power. Any authority for the user to do something is borrowed from the server (which can also remove it at any point).