A license is a document that specifies what can and cannot be done with a work or data (regardless of format). It grants permissions and states restrictions. Broadly speaking, an open license is one which grants permission to access, re-use and redistribute a work with few or no restrictions. A Creative Commons (CC) license is a public copyright license that enables free distribution of work, and is used when an author wants to give other people the right to share, use, and build upon a work. CC0 and CC-BY are most commonly used (and recommended).
CC0 is recommended for all scientifical tabular data, metadata and databases. Although CC0 doesn’t legally require users of the data to cite the source, it does not take away the moral responsibility to give attribution, as is common in scientific research1.
A CC-BY license allows for research to be openly available whilst still ensuring that others give you credit in the form of a citation. This licence lets others distribute, remix, tweak, and build upon work (even commercially) as long as they credit you for the original creation. This is the most accommodating of licences offered. It is recommended for maximum dissemination and use of licenced materials. A CC-BY is the most commonly recommended license. From the Gates Foundation: “Transforming the lives of the world’s poorest people will require the collaboration of many partners, and it is crucial that they can access and use research without restriction. A CC BY license allows users to build upon the research without restriction2“.