The number of times a person must be exposed to an advertising message, in order to drive the desired outcome. Frequency is calculated as the number of delivered impressions per unique user. It’s important to note that multiple exposures to an ad over an extended period of time is more likely to shift a subject’s perception of a brand (and drive desired outcomes), compared with a single exposure. Conversely, too many exposures can reduce impact, alienate prospects, and/or waste impressions. Unfortunately when programmatic players attempt to set ideal brand frequency, they are often leveraging frequency caps, not optimal frequency. See frequency caps versus frequency targeting.