From Science Europe Data Glossary
Definition: source data is data that already exist irrespective of the research that is carried out.
Explanation: source data may be information obtained for other purposes (for example public administration records or clinical data) or physical or digitalized collections of objects and texts (for example digital libraries, text corpora or other scientific collections). Information on the internet may also be considered source data in this context. In accordance with this definition, the results of previously conducted research may also be seen as source data.
alternative definition: source data is raw data that has not been processed for meaningful use to become Information.
See also: primary data; research data