Data include the underlying “raw” information produced in the course of conducting research—so that others can review, repurpose, and/or aggregate that information to improve the quality, utility, and reach of the underlying research, or to build it into something new. The Open Knowledge Definition sets out the meaning of open data as “A piece of data or content 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.”
The National Science Board (U.S.) Committee on Strategy and Budget Task Force on Data Policies Statement of Principles describes Open Data as "the concept and practice that certain data be made freely available, without restrictions, for no more than the cost of reproduction and distribution."
The Panton Principles fo Open Data in Science, state "Science is based on building on, reusing and openly criticising the published body of scientific knowledge. For science to effectively function, and for society to reap the full benefits from scientific endeavours, it is crucial that science data be made open. By open data in science we mean that it is freely available on the public internet permitting any user to download, copy, analyse, re-process, pass them to software or use them for any other purpose without financial, legal, or technical barriers other than those inseparable from gaining access to the internet itself. To this end data related to published science should be explicitly placed in the public domain."
Open Knowledge Foundation What is Open Data?
World Bank Open Data
SPARC Open Data Resources