Four times every year are ratings periods commonly known as “sweeps.” These periods are typically held in February, May, July and November, though the actual dates often extend into neighboring months.

What is sweep week?

It's the result of an anachronism: Nielsen developed the concept of sweeps week in 1954, when they mailed small TV ratings booklets to households across the country and asked them to record everything they watched for a week. ...

What February sweeps?

Local advertisers loathe the sweeps system because it artificially inflates audience numbers, which in turn inflates the ad rates they have to pay. Networks and commission-based ad agencies love sweeps for just this reason, though.