Sweeps periods are those in which Nielsen Media Research, the main ratings-measurement body in the US, simultaneously measures ratings in all local markets.

The sweep months are usually February, May, July and November, and are critical months for networks and local TV stations alike. The figures generated in these months are used by local TV stations and cable systems to calculate advertising rates and to make scheduling decisions. Similar actions take place at the networks when their main primetime lineups are placed under the sweeps microscope.

The term "sweep" now has little relevancy although is still used frequently to discuss the ratings-gathering process in these critical months. It originates from the 1950s, when Nielsen would sweep across the US with ratings survey books starting on the East Coast and moving gradually west.