Define reach, frequency, continuity, and gross impressions.

Reach is the number of people, households, or businesses in a target audience exposed to a media vehicle or message schedule at least one time during a given time period. Frequency is the average number of times an individual, household, or business within a target market is exposed to a particular advertisement within a specified time period. Continuity is the schedule or pattern of advertisement placements within an advertising campaign period. Gross impressions are the number of exposures of the audience to an advertisement.