Theatre performances, typically dramatic or musical, are presented on a stage for an audience, whose expectations about the performance and their engagement with it have changed over time (1). Vaudeville and music halls, for example, were once popular forms of theatrical entertainment popular in the United States, England, Canada, Australia and New Zealand before being superseded. Radio and television, often broadcast live, is a 20th century version of theatre entertainment that exists alongside the traditional forms. Plays, musicals, monologues, pantomimes, and performance poetry are examples from the very long history of theatrical entertainment and performance art. Stand-up comedy is a type of performance usually given in a theatre. The stage and the spaces set out in front of it for an audience create a theatre. All types of stage are used with all types of seating for the audience, including the impromptu or improvised (2, 3, 6); the temporary (2); the elaborate (9); or the traditional and permanent (5, 7). They are erected indoors (3, 5, 9) or outdoors (2, 4, 6). The skill of managing, organising and preparing the stage for a performance is known as stagecraft (10). The audience's experience of the entertainment is affected by their expectations and the stagecraft as well as by the type of stage and the type and standard of seating provided. Vaudeville was a theatrical genre of variety entertainment popular in the United States and Canada from the early 1880s until the early 1930s. Each performance was made up of a series of separate, unrelated acts grouped together on a common bill. Types of acts included popular and classical musicians, dancers, comedians, trained animals, magicians, female and male impersonators, acrobats, illustrated songs, jugglers, one-act plays or scenes from plays, athletes, lecturing celebrities, minstrels, and movies. A vaudeville performer is often referred to as a vaudevillian. Vaudeville developed from many sources, including the concert saloon, minstrelsy, freak shows, dime museums, and literary burlesque. Called "the heart of American show business," vaudeville was one of the most popular types of entertainment in North America for several decades. Television (TV) is a telecommunication medium for transmitting and receiving moving images that
can be monochrome (black-and-white) or colored, with or without accompanying sound. "Television" may also refer specifically to a television set, television programming, or television transmission. The etymology of the word has a mixed Latin and Greek origin, meaning "far sight": Greek tele (), far, and Latin visio, sight (from video, vis- to see, or to view in the first person). Commercially available since the late 1920s, the television set has become commonplace in homes, businesses and institutions, particularly as a vehicle for advertising, a source of entertainment, and news. Since the 1950s, television has been the main medium for molding public opinion. Since the 1970s the availability of video cassettes, laserdiscs, DVDs and now Blu-ray Discs, have resulted in the television set frequently being used for viewing recorded as well as broadcast material. In recent years Internet television has seen the rise of television available via the Internet, e.g. iPlayer and Hulu. Although other forms such as closed-circuit television (CCTV) are in use, the most common usage of the medium is for broadcast television, which was modeled on the existing radio broadcasting systems developed in the 1920s, and uses high-powered radio-frequency transmitters to broadcast the television signal to individual TV receivers. The broadcast television system is typically disseminated via radio transmissions on designated channels in the 54–890 MHz frequency band. Signals are now often transmitted with stereo or surround sound in many countries. Until the 2000s broadcast TV programs were generally transmitted as an analog television signal, but during the decade several countries went almost exclusively digital. A standard television set comprises multiple internal electronic circuits, including those for receiving and decoding broadcast signals. A visual display device which lacks a tuner is properly called a video monitor, rather than a television. A television system may use different technical standards such as digital television (DTV) and high-definition television (HDTV). Television systems are also used for surveillance, industrial process control, and guiding of weapons, in places where direct observation is difficult or dangerous. Some studies have found a link between infancy exposure to television and ADHD.