Your advertising reach is represented by the total number of unique listeners that heard your ad.
It is different than the number of impressions and it is usually lower than that number. The ratio between reach and impressions is generally determined by the type of objective you're setting for your campaign. For a reach or awareness campaign you naturally want as many unique listeners as possible, whereas if you're more focused on conversions, you may want to target a number of listeners with the same ad multiple times.
Audience guide can help you address the perfect audience for you campaign that matches your campaign objective. For more details on how to use this feature please check out our blog.