Pretty much..
For example, if I had a company BestReg that was a registrar, I could give folks the option of becoming resellers for me. This means that tomorrow if you want to start selling any of the services that I do, you can sign up with BestReg and start another site selling some subset of the services that I offer. If you start allowing people to register domain names for example, all those will actually be registered through my company's account with the registry because BestReg is the one allowed to register names. However, to your customers, all this will seem seamless.
Its something like a McDonalds franchise with differing amounts of creative control allowed to the franchisee depending on what the franchise owner wants or is allowed to do.
Hope that helps..
ST Domains
(Rep appreciated if this helped..)