Well-informed choices about how to intervene to improve health outcomes de-pend on access to reliable information, including research evidence. Many peo-ple (not only the public, but health professionals and policymakers too) have problems understanding some of the terminology used in describing evalua-tions of treatments. We have developed a glossary to provide plain language ex-planations and illustrations of 242 commonly used terms. The glossary is freely available at http://getitglossary.org and can be incorporated into documents providing support for evidence-informed healthcare decisions, and embedded in other websites serving a wide variety of functions.