Reach is the total number of people who see your content. Impressions are the number of times your content is displayed, no matter if it was clicked or not. Think of reach as the number of unique people who see your content. In a perfect world, every one of your followers would see every piece of content you posted.
What happens after 10k followers on Instagram?
Once you have 10k followers, Instagram will make it easier for you to get people to your website via Stories with the swipe up to link feature. Swipe up is the only way to get a direct link from your Instagram to your other web properties. And, it’s available in STORIES, if you have 10k followers.