See also: Reach & Frequency

CIMM DEFINITION: The average number of times the unduplicated homes reached are  exposed to a schedule of content whether an ad, a program, a video or a schedule of spots.

2: The number of times a complete electromagnetic wave cycle occurs in a fixed unit of time, usually one second. The rate at which a current alternates, measured in Hertz on a telecommunications medium. (Source: CableLabs)

3: The number of times an ad is delivered to the same browser in a single session or time period. A site can use cookies in order to manage ad frequency. (Source: IAB)