In order to release the data as open it should come with a license. In the open world, there are differente licenses for different purposes (GPL, MIT, BSD licenses for Software - OpenSource; Creative Commons for artwork - sogns, text, images, videos; even GFDL can be used for documentation) but it is not always clear which are the possible license to release correctly data as open.

OpenStreetMap had this issue with its huge database, and changed the license from CC to ODbL. However, if I want to release a dataset, for example a CSV with some information, it is not a database.

Which license can I use?