Apps restricted to users in a specific organization are called private apps. If your organization develops apps (or uses a third-party to develop apps) intended for internal distribution, you can publish them to managed Google Play as private apps.
Private apps published to managed Google Play aren't visible in the public Play store; they're only available to users in the organization(s) you specify. You can distribute private apps to users the same way as public apps—remotely install them or list them in your users' managed Play store.
For information on how to build internal private apps that are optimized for Android Enterprise, see the Build for Enterprise developer guide.