Nielsen ratings are a system used to measure the popularity of television programs in the United States. They provide data on how many people are watching a show, which helps networks and advertisers understand audience preferences. This information is crucial for determining advertising rates and scheduling programs. The ratings are collected through a combination of electronic devices and surveys. Nielsen Media Research selects a sample of households to represent the viewing habits of the entire population. By analyzing this data, networks can make informed decisions about which shows to promote or cancel based on viewer engagement.