Final answer:
Local TV stations that broadcast national network programming and carry national advertising are called affiliates. These stations follow network schedules but can preempt for local emergencies. Affiliates were historically crucial for network distribution but on-demand technology has altered viewing habits.
Step-by-step explanation:
The local TV stations that contract with national networks to provide specified programming during certain hours and carry national advertising within their programming are known as affiliates. Affiliates adhere to a schedule set forth by the network, broadcasting shows such as 'Black-ish' at carefully orchestrated times. However, these stations maintain the right to preempt national programming for local emergencies such as fires or other urgent news. When it comes to reaching local audiences, national networks have traditionally relied on these affiliates for distribution using their transmission towers.
While cable technology now allows networks to reach viewers directly, affiliates remain important for those who receive programming over the air via antennas and receivers. With the evolution of technology, however, on-demand services like Netflix have changed viewing habits by offering content that is accessible immediately and not constrained by traditional schedules.