It does so by providing a number of different licenses that content creators can use to indicate the terms under which content is made available. The licenses range from complete public domain, which allow anyone to use the content for anything, to licenses that only allow non-commercial use, to licenses that allow use with attribution to the original source.
Creative Commons has a step-by-step guide that you can follow to decide which license to use for your works. WP Glossary, for instance, is licensed under the Creative Commons Attribution 4.0 International, abbreviated CC BY 4.0. Under that license, you’re free to share and modify the content however you want, as long as you give appropriate attribution to the source of the content.
Creative Commons was founded in 2001 by law professor Lawrence Lessig.