Open data is data that is accessible to anyone and that can be used, disseminated and reused by anyone for any purpose. The demand to make data available in the sense of open data is based on the assumption that freely usable data leads to greater transparency and collaboration. In the case of public sector data, an additional argument is that the collection/creation of the data is financed by tax revenue and must therefore be made available to the general public in return.

Restrictions on use are only permitted in order to safeguard the origin and openness of the knowledge, for example by naming the author or using a share-alike clause. Free licenses are used to ensure reusability. The Open Data movement is part of the knowledge revolution and shares many arguments with the related topics of Open Source, Open Content, Open Access and Open Education. The provision of open data by the public sector is seen as a prerequisite for open government.

Examples of open data include teaching materials, geodata, statistics, traffic information, scientific publications, medical research results, and radio and television broadcasts. In addition to data held by government agencies, open data can also include data held by private-sector companies, universities and non-profit institutions.