A browser extension is a computer program that extends the functionality of a web browser in some way. Depending on the browser and the version, the term may be distinct from similar terms such as plug-in or add-on. Extensions can be created through use of web technologies such as HTML, JavaScript, and CSS. Browser extensions can also improve the user interface of the web browser with out directly affecting viewable content of a web page. This improvement can be achieved through a variety of add ons such as toolbars and plug-ins.