Software that renders HTML pages (Web pages). It turns the HTML layout tags in the page into the appropriate commands for the operating system, which causes the formation of the text characters and images for screen and printer. Also called a "layout engine," a rendering engine is used by a Web browser to render HTML pages, by mail programs that render HTML email messages, as well as any other application that needs to render Web page content. For example, Trident is the rendering engine for Microsoft's Internet Explorer, and Gecko is the engine in Firefox. Trident and Gecko are also incorporated into other browsers and applications. Following is a sampling of browsers and rendering engines. See HTML and render. RenderingBrowser Engine Source Internet Explorer Trident Microsoft AOL Explorer Trident Microsoft Firefox Gecko Mozilla Netscape Gecko Mozilla Safari WebKit WebKit Chrome WebKit WebKit Opera Presto Opera Konqueror KHTML KHTML.