High-frequency direction finders (HFDF) are radio navigation devices that intercept and locate radio signals. There are many synonyms for HFDF, depending on the context and application. These synonyms include radio direction finders (RDF), radio direction finding (RDF) systems, Direction Finding (DF) equipment, radio locators, radio bearing systems, and radio tracker systems. In military and intelligence contexts, HFDF is often called signals intelligence (SIGINT) or electronic intelligence (ELINT) equipment. Other possible synonyms include radio wave direction finders, radio signal detectors, and radio wave trackers. Regardless of the term used, HFDF technology plays an important role in navigation, surveillance, and defense operations.