I believe this means to sell it on to clients so that they can use it under your brand (not the actual builder). e.g. WebPresences develop sites for website designers.
Generally it means to replace references to WordPress in the admin, i.e. login screen, admin bar etc.
Some website designers use this, I update the logo on the login screen but refrain from trying to "hide" WordPress as I value WordPress and what it allows me to do.