Hybrid virtual currency

Definition
A hybrid virtual currency is a virtual currency system where "one or more of the flows between the virtual currency and real dollars or goods and services is closed."

Overview
For example, participants can purchase virtual currency with real dollars or earn virtual currency by completing tasks, such as taking surveys, and then use the currency to purchase real or virtual goods and services. However, the virtual currency might not be exchangeable back into real dollars. An example of a hybrid system is some massively multiplayer online role-playing games (MMORPG). MMORPGs allow users to create avatars, or graphical representations of themselves, that exist within a digital world and interact with other avatars around the globe to carry out tasks.

Source

 * "Overview" section: Virtual Economies and Currencies: Additional IRS Guidance Could Reduce Tax Compliance Risks, at 4.