Data Licenses 

A license specifies how your data can be re-used by other people.

Many people use 'Creative Commons' licenses to give a clear signal to other people about how the information and content they have been created may be re-used. Creative Commons are Copyright licenses, and so do not apply to datasets (which are generally regarded as 'collections of facts' and thus not under copyright, but often under other Intellectual Property restrictions). However, Open Data Commons provide a number of licenses that can be used for datasets. 

The Open Data Commons licenses are based on the Open Knowledge Definition (OKD). Data.gov.uk are aiming to make most of their datasets available under OKD Compliant licenses. 

Even if not using an Open Data Commons license, see their FAQs and guide for details of how to apply a license to a dataset.