Fast Healthcare Interoperability Resources (FHIR, pronounced "Fire") is an MnM project, initiated in September 2011. Prior to it becoming a HL7 project this work was known as Resources for Health (RFH), a "fresh look" proposal by Grahame Grieve, which he made made on August 18th, 2011.
FHIR defines a set of "Resources" that represent granular clinical concepts. The resources can be managed in isolation, or aggregated into complex documents. This flexibility offers coherent solutions for a range of interoperability problems.
The simple direct definitions of the resources are based on thorough requirements gathering, formal analysis and extensive cross-mapping to other relevant standards. A workflow management layer provides support for designing, procuring, and integrating solutions.
Technically, FHIR is designed for the web; the resources are based on simple XML, with an http-based RESTful protocol where each resource has predictable URL. Where possible, open internet standards are used for data representation.
The initial definition can be found here.
The content is being moved into HL7