The Science Glossary from Vision Learning is an excellent free app for your iPhone, iTouch or iPad. This extremely useful app provides an extensive glossary of several hundred scientific terms and definitions, with easy to understand text. The app also includes loads of mini-biographies of influential scientists from all over the world. Technical terms within each glossary definition are linked to related definitions, providing easy navigation through the app. And many terms are linked to the learning modules on their excellent website, allowing you find out more about each topic.