Actually there are several. Defining Health2.0 is also a user-generated phenomenon. You can choose your own definition.

Health 2.0: "New concept of healthcare wherein all the constituents (patients, physicians, providers, and payers) focus on healthcare value (outcomes/price) and use competition at the medical condition level over the full cycle of care as the catalyst for improving the safety, efficiency, and quality of health care"

Medicine 2.0: "Medicine 2.0 applications, services and tools are Web-based services for health care consumers, caregivers, patients, health professionals, and biomedical researchers, that use Web 2.0 technologies as well as semantic web and virtual reality tools, to enable and facilitate specifically social networking, participation, apomediation, collaboration, and openness within and between these user groups.

http://health20.org/wiki/Health_2.0_Definition