This question measures if anyone is legally allowed to use, modify and redistribute data for any purpose. Only then data is considered truly "open" (see Open Definition). Answer ”Yes” if the data are openly licensed. The Open Definition provides a list of conformant licences. Answer also “Yes” if there is no open licence, but a statement that the dataset is in “public domain”. To count as public domain the dataset must not be protected by copyright, patents or similar restrictions. If you are not sure whether an open licence or public domain disclaimer is compliant with the Open Definition 2.1, seek feedback on the Open Data Index discussion forum.