Reach
The number of different people who saw a post, story or ad at least once.
Reach counts people, not views. If 10,000 people saw a post and some of them saw it twice, reach is still 10,000. It is the honest measure of how many people a campaign actually got in front of.
Reach is reported by the platform, so for influencer posts it has to come from the creator, as a screenshot or a shared insights export. Ask for it in the contract and set a deadline, usually 7 days after posting for feed content and 24 hours for stories, which expire from insights.