Open core is freemium. You can use the base under a free license but if you want fancy features, those are under a non-free license.
Selling exceptions (or what someone else called, "dual licensing") means everyone gets the same software, both free and non-free, but people who don't want copyleft have to pay.
Selling exceptions (or what someone else called, "dual licensing") means everyone gets the same software, both free and non-free, but people who don't want copyleft have to pay.