Short answers, pulled from the story.
A television broadcaster or television network is a telecommunications system that distributes programming from a central operation to many individual television stations simultaneously. A television station is a single transmitter or facility that receives and rebroadcasts that programming, while a network is the overarching distribution structure connecting many such stations.
The DuMont Television Network launched what Newsweek described as "the country's first permanent commercial television network" on the 15th of August 1946, connecting New York City with Washington. NBC followed on the 27th of June 1947 with what it called "the world's first regularly operating television network", serving New York City, Philadelphia, Schenectady, and Washington.
The BBC opened the world's first regular high-definition television service on the 2nd of November 1936, transmitting from a 405-line transmitter at Alexandra Palace in London. Experimental broadcasts using John Logie Baird's electromechanical 30-line system had begun in 1929, with limited regular broadcasts starting in 1934.
Fox Broadcasting Company launched on the 9th of October 1986 after Rupert Murdoch's News Corporation purchased the television assets of Metromedia. By 1994 it had risen to the status of the fourth major American network alongside ABC, CBS, and NBC.
Bell Telephone Laboratories patented coaxial cable in 1929, and its ability to handle a frequency band of 1 MHz made it capable of carrying television signals over long distances. AT&T laid the first coaxial cable between New York City and Philadelphia in the 1930s, and by 1951 the four major American networks stretched coast to coast on AT&T Long Lines' microwave radio relay network.
Only three national over-the-air television networks are currently licensed by the Canadian Radio-television and Telecommunications Commission: government-owned CBC Television in English, Ici Radio-Canada Télé in French, the private French-language network TVA, and APTN, which focuses on Indigenous peoples in Canada. CTV and Global are generally considered national networks by coverage but are not officially licensed as such.