A television advertisement or television commercial (often just commercial (US) or advert or ad (UK) or ad-film (India)) is a span of television programming produced and paid for by an organisation that conveys a message. Advertisement revenue provides a significant portion of the funding for most privately owned television networks. The vast majority of television advertisements today consist of brief advertising spots, ranging in length from a few seconds to several minutes (as well as program-length infomercials). Advertisements of this sort have been used to sell every product imaginable over the years, from household products to goods and services, to political campaigns. The effect of television advertisements upon the viewing public has been so successful and so pervasive that it is considered impossible for a politician to wage a successful election campaign, in the United States, without use of television advertising. A radio commercial (in the USA also called a spot by people in the business) is a form of advertising via the medium of radio. Airtime is purchased from a station or network in exchange for airing the commercials. typically airing their commercials within. Today [in the USA, at least] sponsorship is comparatively rare, the selling of spots being the predominant practice. Radio commercials are usually sold in 10, 20, 30, 60 or 120 second increments. When sponsoring a program, in the USA the 10 seconds or so in which the sponsorship is acknowledged before and/or after the program, is called a “billboard.” Often, the sponsor’s commercial will air immediately after the billboard. While radio has the obvious limitation of being restricted to sound, proponents of radio advertising often cite this as an advantage, the "visual" portion being supplied by the listener's unbounded imagination.