Definitions for "External Viewer"
An external viewer is an additional piece of software that "helps" your browser interpret and display specific file types that it doesn't have the built-in ability to do itself.
An application for viewing multimedia information, such as audio files, within Web pages. External viewers are available for audio, video, and virtual reality data, among many others.
An external viewer is an application called by a browser to display types of graphics, video or audio not otherwise supported by the browser. In Netscape Navigator, viewers are configured using the Helper Applications tabsheet of the General Preferences property sheet on the Options menu. In Internet Explorer, most standard viewers are pre-configured using File Type registration, which is accessible through the Options property sheet on the View menu.