Reach refers to the number of people who see an ad or a campaign.
Reach, as a metric, refers to the estimated number of people it is possible to reach through advertising channels, or any promotional campaigns.
While the reach represents the number of people who have seen an ad or a piece of content in a campaign, the impressions refer to the number of times the content itself was seen.
To make it easier to understand, if a website runs an ad, and it was seen by 1000 people, then the reach is 1000. But if the ad was displayed 5000 times, then the impressions will be 5000, since a person can see the same ad multiple times.
All metrics play a huge role in website and campaigns' analysis, so here's why is the reach essential to track:
Reach can fall into multiple categories on multiple distribution channels; here are some mediums that provide the reach of a piece of content or ad: