"Freemium" is a combination of the words "free" and "premium." It refers to a business model where a product or service is offered for free, but additional features or content require payment. Full definition
I can give you many examples of freemium games in Asia that now have made more than a billion dollars in lifetime revenue. (mcvuk.com)
Lexum's main thinking today is to adopt some sort of freemium model, where what is there is for free and something more will call for subscriptions. (slaw.ca)