Frequency

How often the same individual is exposed to an ad or marketing message. Frequency is typically the conjoined twin of reach (see also: Reach), as well it should be.

Without determining frequency, an ad could achieve 1 million impressions by reaching the same person 1 million times.

With a frequency of one, in that a person is only exposed to the ad one time, then the advertiser achieves 1 million impressions by getting in front of 1 million people one time each.

Typically, the desired frequency is more than one but less than a lot. Relatively few people respond to an ad after a single exposure, but after too many exposures, the advertiser will typically experience diminishing returns.