Open Data definitions
The Open Definition sets out principles to define ‘openness’ in relation to content and data and can be summed up in the statement that:
“A piece of content or data is open if anyone is free to use, reuse, and redistribute it — subject only, at most, to the requirement to attribute and/or share-alike.” http://opendefinition.org/
Open data at Linked Gov “Open data is non-personally identifiable data produced in the course of an organisation’s ordinary business, which has been released under an unrestricted licence (like the Open Government Licence).”
The Open Government Licence for Public Sector Information
http://www.nationalarchives.gov.uk/doc/open-government-licence/
Open Data Commons Open Database License (ODbL) http://opendatacommons.org/licenses/odbl/
also being adopted by Open Street Map
Open Knowledge Foundation http://okfn.org/about/vision/