A guest host (or guest presenter in the United Kingdom) is a host, usually of a talk show, that substitutes for the regular host if they are, for example, ill or have other commitments. Although guest hosts are often undesirable, some shows have seen the guest host do a better job than the main host, and filling in as a guest host has helped to launch the careers of a variety of television and radio talents. In U.S. radio, the concept of a guest host is known as a "swing jock".