What main aspect does reach focus on?

Reach primarily focuses on the number of distinct individuals exposed to an advertisement. This metric measures how many unique users or potential customers have seen the ad at least once during a specified period. Understanding reach is essential for marketers because it helps determine the potential audience size and gauge the effectiveness of an ad in spreading brand awareness. High reach signifies that the advertisement has successfully penetrated a larger segment of the target market, indicating broader visibility and greater opportunity for engagement.

While the other options pertain to relevant advertising concepts, they do not specifically define reach. The period an ad is active relates to timing, the diversity of the target market involves audience segmentation, and total exposure of a single ad refers to frequency rather than reach. Therefore, the focus on distinct individuals emphasizes the importance of unique impressions in evaluating advertising success.