Freemium
URL = http://en.wikipedia.org/wiki/Freemium
Definition
From the Wikipedia:
"Freemium is a business model which works by offering basic services for free, while charging a premium for advanced or special features. The word freemium is a portmanteau created by combining the two aspects of the business model: free and premium. The business model has gained popularity with Web 2.0 companies." (http://en.wikipedia.org/wiki/Freemium)