This is the number of times unique accounts saved your posts.
Users have the option to save a post to go back to at a later time. This can be found in the ‘Saved’ section of their profile. Saved posts can be an indication of how interesting or relevant your content is to your users. It is a great feature because users can re-visit your content months later, leading them back to your brand!
Historical data for Saved is available for Instagram business accounts up to two years, or since converted to a business account.