Enterprise accounts, that are sometimes called corporate, are designed for internal company use such as sharing memos, private group chat or as a simple project and task management system.
Enterprise accounts can also be programmed to integrate more complex functionality and they are becoming increasingly popular within China organizations. Also, in order to keep such internal networks secure, followers have to go through authentication process. This is quite unlike other accounts types where gaining more followers is pretty much the point.
Obviously, those accounts are not designed for marketing outside of a company.