Final answer:
Network advertising is when an advertiser purchases airtime on a national network, and the content is distributed nationwide via local affiliate stations.
Step-by-step explanation:
When an advertiser purchases airtime from a national network, and the commercial is transmitted across the nation through the affiliate station network, this type of advertising is known as network advertising.
A local station that broadcasts national network programming is known as an affiliate. An affiliate, by agreement with the network, follows a schedule provided by the network for airing programs and commercials, with deviations only for urgent local or national emergencies.
Before technologies such as cable and fiber optics, networks required affiliates to reach different markets via transmission towers. With technological advancement, networks can now also utilize cable stations to directly reach viewers without airwave transmission. Cable technology allows for specialization in programming, targeting specific demographics, which is beneficial for advertisers looking to connect with a distinct audience.