Reach is a term used in the context of online advertising to refer to the number of unique individuals or households that have been exposed to an ad campaign. Reach is typically measured as the number of unique users or devices that have seen an ad, and can be used to evaluate the scope and scale of an advertising campaign. Reach can be an important metric for advertisers, as it can provide insight into the size and reach of their target audience, and can help to assess the effectiveness of their media planning and buying strategy. Reach can also be beneficial for publishers and platforms, as it can provide insight into the performance and value of their ad inventory, and can help to optimize the monetization of their audience. Reach can be measured and reported in a variety of ways, such as impressions, views, or other engagement metrics, and can be an important part of an advertiser's performance reporting and analysis.