Open Data are those data sets that are available to the public and can be reused and returned to publish without restriction. It has a spirit similar to that of other movements "Open" and communities as open source hardware free, open content and open access. Practice and ideology of open data itself are well established for some time, although the term "Open Data" is recent and associated Internet and World Wide Web.

According to the Open Knowledge Foundation content to be opened should follow three principles: should let the public the right to use it, the right to reuse and adapt it to the needs and the right to redistribute and share it. The only restriction is that the final product should also follow the principle to be open.

The data are distributed in an open format that allows manipulation technique without restriction under open source license and / or terms and conditions that do not prevent end users review, remix and redistribute them to third parties.

The data should satisfy certain conditions associated with your description, traceability, quality, privacy and interoperability.

Source: Wikipedia