Tellurium is a UI module based web testing framework. The UI module is a collection of UI elements you group together. Usually, the UI module represents a composite UI object in the format of nested basic UI elements. The UI module makes it possible to build UI elements' locators at run time. The framework does object to locator mapping (OLM) automatically at run time so that you can define UI objects simply by their attributes and write your selenium tests just like writing JUnit/TestNG tests. Since the framework constructs the actual locator automatically at run-time and it uses the Group Locating Concept (GLC) to exploit information inside a collection of UI components to help finding their locators, Tellurium is more robust, flexible, reusable compared with the Selenium testing framework.
This is a short version.